Thanks for the answers you both and thanks for the compliment, mourner!
I removed my mould lines with a micro swiss pocket knife, which has quite a sharp blade, following one of the articles on this site. That was quite a time-consuming work, so I guess I will try out sandpaper as an alternative!
Concerning assembling: Yes, I thought I would find some way of using sticks or something to put the parts on - unfortunately, I found no satisfying way of doing so, so I just held every little part in my left hands fingers while painting (and yes, that was ...not easy

).
About using the milliput after priming and basecoating: Yes, I somehow thought that\'d be a bad idea, but I didn\'t have the heart to try it before starting to paint...however, when I saw that the gap was really visible even with the two or three layers of paint on it, I thought I would give it a try. Will be smarter next time!
For priming I used sprayed chaos black, too, although that was difficult too, because the parts just flew away when hit by the spray - I did not hold them in my hands because that would really have resulted in a fething taint of chaos on me! lol Therefore, assemblying the parts as far as possible and somehow mounting them on something will be steps I\'ll think of when doing the next marine.
I guess I\'ll start painting again when I come home from work, starting with a new layer for the blue servo armour, so I may be able to give an update with pictures in the evening!
Witzkatz