A tip re. engines.
I usually lay out the size of my ships when I start a game beforhand.
Say: 6000 ton DD, 9000 ton CL, 12000 ton CA, 24000 ton BB, 36000 ton DN
Ships get 25% engines, so I design a 750 ton engine. DD gets 2, CL 3, CA 4, BB 8 and DN 12
Note:
By the time I am ready to have BB and DN rolling off the assembly line, I usually design a dedicated engine (in that case a 1500 ton engine) for those, but I _could_ use the standard 750 ton ones.