Where would I look to find out what the minimum radius track a loco or cars needs in order to operate correctly?

From reading previous posts I see that some cars do not like 18" vs 22" curves.  When designing my track I want to be sure all my cars and the new loco I am about to buy will run smoothly.

Thanks.

I have a rather large village and want to run a rather large train up to 12 cars.  Is there any suggestions about where I can find information about how much HP a train has?  Is a diesel loco better than a steam version?  The current units I have seem to drag when I put that much behind them.  Also want to perhaps climb an incline up to 3 inches over 12 feet, so I know I would have a problem with my current units.
Thanks in advance for your knowledge.