[bardd]

1. As a whole your idea sounds good. it should work well. One thing that troubles me is the wheel setup. How will you connect the sprockets to the center wheel? Both on the same side? One on each? If you put them on the same size, I can almost guarantee the chains will get on top of one another and get stuck. We lost our entire 2012 season that way. Your best bet would probably be to put them in different sides, which might interfere with the gearbox... But if you plan correctly it would work.
   
2. I have no experience with #25 chains, but many teams in Israel use them for drives, and I haven't heard of a chain breaking yet (I've made some research when we thought of moving to #25 chains). They're weaker but will probably hold. If you're not sure, hang one from the ceiling and have a... "big" person hang off it, see if it breaks (with a helmet and safety goggles, just in case).