I'm trying to build a back story for my Astropath whom grew up on an imperial world.

good for you!

What I want to know is; after reading the description in character creation over and over again.

What kind of government rules in the 40K universe?

Its effectively a devolved dictatorship. The dicatator being a rotting carcass bound in a arcane-technological machine that acts as a lighthouse. The actually day to day running of the Imperium (if with the vagarities of warp travel such a thing exists) is done by the High Lords of terra, who are representatives of the various organs of state. The most important of which paradoxically is the master of the administratum, who is the boss of the Imperiums bloated, monolithic and ossified bureaucracy -the scribes and pen pushers who keep a impossible tally and toll of all the data. Its so bad that a administrative error can lead to whole worlds being forgotten or ignored, or relief efforts arriving centuries out of date. The planets pretty much are at all different levels of technology and society, but there is usually one guy- a governor that answers to the imperium. This could be a elected president, a feudal like emperor, a sector spanning imperial noble of some standing, or just a guy sitting in a space station over a world where feral humans scrap for resources or any number of variations. The tying factor is that depending on the planets classification all of them have a tithe to pay to the imperium which again varies on the planets class and politics.

I'm pretty sure it's more of a dictatorship, than anything else. I would like someone to tell me what it would be like for an imperial citizen in their every day life.

The default mode that is presented by Games Workshop is " Serfs in space', that is to say everyone is kind of a peasant owing fealty to a feudal lord, which crops up in the literature and backstories again and again. However it is really up to you. You can create a world not too disimilar to our own, where the imperium is a distant tale whispered by conspiracy theorists. Its up to you.There are various classes of imperial worlds. A man or woman living in a hive world will have a different experience than one living on a feral world. The basic concept that goes its that there is a vastly different types of planets and societies

Are males and females treated equally?

Again depends on the planets classification and varies with societies. But as the default fluff of the imperium is feudal in nature, I would in the stories women sadly usually take a second to men, but hey basic GM is market orientated towards the 14-18 teenage boys range. However as a Astropath there should be no problem. They are too valuable to the imperium to be treated with anything else but respect and not a bit of trepidation irrespective of gender. As part of a rogue trader crew the distinction between men and women is almost nil. Each one survives on the merits and skills.

How is the education of lower classes, middle classes, high classes and orphans? When you are born, does that make you a citizen? Or do you have to serve time in the military?

Varies with planets- Far too varied, but as a default mode I would say:

Education:

Lower: Zero to poor- with some sunday school training from missionary zealots who preach the greatness of the undying emperor. Again think peasants in space.

Middle: Slighly more. Think belonging to a merchant guil and learning the skills of your familys trade on a planet.

High Classes: medium to ridiculously high. A backwater noble is hardly going to get the same training as a a scion of a majour sector house. For details see the Inquisitors handbook to get idea of the skill sets noble tend to learn, like diplomacy and such like.

Orphans: Either zero to poor, with the exception of the orphan sons of major imperial servants: They tend to go to something called the schola progenium, which is kind of like a jesuit School in space, that turns out Inquisitors, commissars and storm troopers etc.., people who are almost fantaically devoted to the imperiums cause (with one famous commisar being the exception) Again for futher details try and find a copy of the Inquisitors handbook.

Citizenship: Technically you are being human makes you an Imperial citizen and yes that includes Space Marines Ratlings Ogryns and 99% machine techpriets, unless you turn into a mutant or traitor or a raw psker in which case you have the legal rights below that of a germ- the exception being sanctioned psykers and navigators.The reality is that its a brutal galaxy and if you are on the lower social rungs no one gives a **** if you live or die, only how productive or usefull you are to the greater Imperium. Human rights are sooo 2K.

Military: Depending on the planets class... Some of them because of their class are required to assemble a PDF- not a computer document but a 'planetray defence force'. Also as part of their tithes some planets, again depending on their class are required to creme off their better soldiers to serve in the imperial guard where they get transported to some hellhole and are expected to clog the opponents guns with their bodies. Thats right... in the table top game the cannon fooder grunts that die in droves are the elite, only really bettered by storm troopers or the elites that survived clogging the opponets muzzles. I seem to remember reading somewhere that one in ten of the PDF are tithed, but I may be wrong.

Being an Astropath, what would happen if the Psycher were to fail the soul-binding procedure and live?

You become a astropath 'after' the soul binding procedure. And thats because you were deemed not strong enough to hold the temptations of the warp on your own and need to 'be one with the emperor', that is to say immunised. If you fail you are usually dead burnt out husk or just plain mad and are probably put down.. I seem to remember there being something about the adeptus astronomica...but I cant bring it to mind.

What about being fed to the Emperor?

Ah thats if you are a psyker and A) You're not good enough to be a sanctioned psker and B) Not good enough to be a astropath. In which case you are plugged into a arcane machine and leeached dry to feed tha master of mankind. Quite grim when you think that even children are subjected to this. Apparently the Emperor has a voratious appetite, although to be fair in a whole millenia he hasnt put on any weight.

A little bit of background about that question: My astropath "Didn't make the cut" and was going to be fed to the emperor, when he walked out of there soul-bound to the emperor instead.

Mmmmm not sure what you are getting at. You could be putting it down to a delayed reaction. Im not sure if they feed ones that have been through the soul bounding procedure back to the emperor. You could put it that just as they were going to strap your astropath into the machine, the soul binding kicks in with a vengence. Then you could say that they the relative time spent non soul bound, made you him/her not quite unsuitable for the astropathic choir singing and metal e-mailing. Soul bound but having too much of a restless spirit. Hence thats why you were bundled on a rogue trader ship. You prefer it out there on the galaxy fringes. Or something. Maybe others have a better idea.

What is life like for a potential psycher on a black ship if you came peacefully, or if you were taken kicking and screaming?

Apparently its grim. If you can get a hold of the the Inquisition war Triliogy by Ian Watson (I think the first book Draco/Inquisitor) It has a description of the ship. Some of them are aware of whats going to happen, other have no idea. You get treated as if you are a live stick of dynamite whaether you go peacefully or not. A bit a like raw unprocessed substance, whch has to be refined. That which can be used, and they are few, are made into psykers which are barely tolerated but vital to the Imperium. The vast majority get used as emperor petrol to keep the astronomicon beacon going. If you cause them any more problems major problems while in a black ship, unless they think youre something special they are just going to incinerate you. Pleanty more out there...infact the inquisition struggles with too many pskers and deviant witches. They have no patience for kicking and screaming.

Anybody out there remember what the Adeptus Astronomica is about, I know that they are the choir singers that make the astronomicon 'brighter' but I cant rememeber where they fit in the whole psyker soul binding procedure, if they are indeed bound

See, i thought (That's what i get eh?) that while on the black ship there were classes etc. probably thinking too fluffy for 40k with that half baked idea.

I can see them dopeing you, tossing you in a void cell and saying "if you twitch, you will meet the emperor soon enough."