Perth might have different plans, but the way we've done it is - You don't have to keep ordering for that +1 industry, that's just saying it will arrive in 3 turns, same for the ships construction etc.
The only limits we have on ships and army sizes is your bank balance. If you're economy can support more and you want more, go for it. I'd say specify large or small for the boats.
I'm not too sure on the 1/5 for the infrastructure myself.
Yes, you can specify for army or naval tech increase - Building more Military bases or developing new tech will achieve this.
You built infrastructure, industry, and 2 large ships last turn, so yeah, that probably cost about 340 gold.
