I think it's possible. You can edit the RS_MaxShipSlots[race]0 files for each race. Just make the base value less and nobody should be able to have enough fleet cap to make capitalships at start of the game. Not sure if you have to change the perLevel upgrade as it's 150%, meaning base of 100 x 1.5 = 150 starting cap. so play around, see what you get. Anyway, that's where I'll start with your idea.
What? What are you talking about sir? What my good man Kilsonx said can't be done, it appears that every capital ship will always cost one Crew point. So the only way to implement what he said, would be to do what I said, and what you unnecessarily repeated in the first half of your post.
The second half of your post is just incoherent. 150% of what? Each level of the Fleet Supply, if thats what you are talking about, can be altered. You could have it start at 1, then jump up to 1,000 for the first level, then 1,001 for the next. Every level can be different. Although I fail to see the link between this and the Capital ship crews Kilsonx is talking about.
And Kilsonx, hey, no problem, I hope you can use that post to achieve the effect you want. Good luck, and any other problems don't hesitate to post.