How does the mechanicus implant trait work exactly? Do I have to buy each implant separately? Do I choose one at character creation stage? Or do I start with all those implants already implanted on me?

The way I understand it is, the trait means I already have those implants installed on my character, except that my character is not very efficient at using them at all. I remedy that by buying the apropriate traits for each implant separately (feedback screech, ferric lure, etc...).

We're all new to the game, and some of us are even new at roleplay games. Our GM saw it as this: I pick ONE implant for free at character creation (I picked electoo inductor). Then if I want to get a new implant from the list in the mechanicus implant trait chart, I need to pay 250 XP, and find someone who has that implant and the skill to install it on me (a mechanicus medical facility perhaps?).

But I'm thinking, man, that's kinda rough, it can't be that way, because then, why aren't psykers returning to earth to be trained in new psychic powers each time they want a new one? Why aren't assasins going back to a culexus temple to be further trained in handling two weapons, or firing at 2 different targets 10 meters apart?

I really hope I'm right and he's wrong, because I really want to use traits like ferric lure, energy stash and such, but ****, paying 250 XP, the implant cost in thrones, waiting to heal, and then paying for the trait itself again? I'd rather go with another class!

You're right, he's wrong. Those implants do next to nothing on their own, they are the foundation upon which your mechadendrites are installed and your tech priest specific talents work.

Some of them wouldn't even work without the rest of the implants. The electoo inductors for example. So you have wires for transmitting power implanted in your flesh? Where from? Where to? How do you control it?

You need all of it for any of it to work properly, your GM is plainly wrong on this issue and I'd switch class if he doesn't see reason.

Another question.

Are the basic characteristic advances cumulative, or aditive?

Case 1: One of our players says they just add +5 each time you buy one. Say, I buy first willpower advance, I get +5. Then I buy a second willpower advance, and I get +5 more, for a total of +10. If I buy a third willpower advance, I get another +5, for a total or +15.

Case 2: The way I understand it. If I buy the first one, I get +5. If I buy a second one, I get +15 (+5 from first and +10 from second). If I buy a third, I get +30 (+5 from first, +10 from second and +15 from third).

Basically:

Case 1: You get +20 after buying all 4 characteristic advances in any one attribute.

Case 2: You get +50 after buying all 4 characteristic advances in any one attribute.

Who's right and who's wrong here?

You get +5 each time you buy an advance, for a total maximum of +20 for any given characteristic.