I am building up my navy - but wonder, whether it is really worth. It is quite costly in purchase and upkeep. Pls give advise.

If you don't have a navy and the other guy does, you're gonna take a much bigger pounding. All of his attacks will do more damage, and he'll be able to field more planes than you. I'd say it's worth it. Except battleships, don't keep them in a time of peace.

Yeah i'd say thats pretty much the way to go.

What would you all consider a good Navy ratio or combination?

Basically what is a good standing fleet to have?

All (except battleships) or nothing imo. A handful of ships won't last long, the more lopsided navy strengths are, the more casualties (on the weaker side). 20 ships will be torn apart by 60 ships in just a few days. That's also why I laugh at people who buy nothing but aircraft carriers.. it's pointless.

I think that if you won't be going into a war for ~3 months, you don't need to keep a large navy around. Personally I keep aircraft carriers and some of the cheaper to maintain ones. You can always just buy them back when war alerts pop up.