Sounds wonderful! I'd be dropping hints like crazy about who (ahem) might do a brilliant job of managing the program...

While five grand sounds generous, I wouldn't necessarily splurge on new bikes. For a program like this, I'd buy up MTBs and cruisers of decent quality and 26" wheels. Buying one size of (slick) tire and one size of tubes ought to simplify matters.
How many bikes would be used by the co-op?