Thanks guys.
I didn't use any external print files or services. I built the 3d models in Blender mainly referring to pictures of actual models I found on the net. I made a few changes to match the ships more with their artworks in the fleet lists, like slightly altered proportions, the different prows of the imperial ship classes and so on.
The ships are printed at home. I know that I could get higher quality prints using print services. But I mainly wanted to know what I can do and how far I can go with my home 3d printer. Part of this little project was to be completely independent from any source (GW or eBay, hint). So the only thing I bought was a BFG rulebook at an online bookstore in England.
Funny thing. For the first two cruisers I used original GW flying stands that I had in my spare part box. Guess what. It didn't take long before the first broke off. So I finally switched to printed flying stands with metal pegs. No more broken stands for me.