Are there rules for how players are seated and next to whom?

Not to my knowledge, nor was there in 3rd edition.

If it helps, I recently updated my race-choice tool...

http://www.mygurps.com/TwilightImperium.html

...to include the option to randomize player order as well.

I think house rules regarding selection of races and arrangement of home systems is practically required. In the rule book I have, it simply says "players select races" but doesn't give you any indication as to how you resolve issues with that. If two people both want the same race, presumably you flip a coin or something, or if you're more OCD, like me, you come up with a draft order for the races.

As far as which position each player's home system goes in, I don't believe it gives any instructions on exactly how that's decided, officially, either, so you're on your own to come up with something that's agreeable to everyone. Technically the instructions DO state that each player will know where their home system is when placing tiles, but I personally would like to agree not to allocate the home systems until AFTER you've built the galaxy map first, thus giving people less ability to hurt others with their tile placement and less ability to help themselves. Then after that you could randomize the home systems, or randomize the order in which people choose them, etc.

I like random, after-the-fact home system positioning, personally. I mean generally, the inhabitants of a galaxy are not going to be able to decide where the supernovae and asteroid fields are, so it feels kind of wrong to allow people to place that stuff in ways that help themselves and hurt other players on purpose, to me.

What we do is give each player two random races to choose from, with those discarded by other players also eligible. We roll dice for initiative when building the galaxy, determine the actual HS spot randomly (forces players to build a balanced galaxy), seat ourselves conveniently and roll again for Speaker.

In 3E we typically chose races randomly (picked from the 10) and we rolled a die to determine where you sat.

The one game of 4E I've played so far I let the other players choose in order of arrival. You got a benefit of showing up on time ;-) I see that changing as we play more games, but it worked alright for that intro game.

Generally, my group shuffles the home systems face down and deals out three or four home systems to each player, with those being the ones you are able to choose from. Seating is, "Which chair did you sit down in when you showed up to play?"

Fairly simple . If we have fewer players we may deal a larger number of home systems to everyone, but generally we don't do more than four.

In 3E, we would include the Lazax Mecatol Rex in the shuffle, and the person who got it would return it and get two more races to pick from in exchange, as a sort of fun little bonus. But since we don't have one in 4E, we can't do that anymore.

My group simply shuffles and places home systems to randomize every game. Quick and easy.

But being strategic when creating the galaxy is part of the fun! Usually when I play we determine seating before galaxy creation. And anyone who makes ****** placements of red-bordered systems usually get screwed with back by the disenfranchised player or by the other players. Kinda like a self regulating communal ethics thing. We usually call it Cosmic Karma.

[Edit] Really, FFG? "Dou" followed by "che" is a worse word than "screwed"?