[cj3958]

A lot of people have already said this, but as far as chain goes, use #35. Especially since its off season. You can get away with #25 if you know what you are doing but you will be constantly fighting it. For example, if your chassis deflects(as all chassis do) then the center to center distance on the axles(and therefore the sprockets) will either get bigger or smaller. When this happens, #25 chain is much more likely to jump than #35. If you are clever and manage that problem you can use #25, but it needs to be taken into careful consideration. IMHO it is not worth it.

As to what size sprockets, it all depends on what gear ratio you want. I would use the JVN gear ratio calculator and put in the gearbox you want to use etc. to determine the best sized sprockets for your application. The important thing is to get enough wrap around the sprocket and to have the correct ratio so that you don't burn out motors.