As long as you don't mind linking several Kindles/Kindle apps to the same account, you should be able to share books across them. If you charge the account with vouchers instead of linking it to a credit card, you'd be safe from users going on a spending spree.
1. No need to touch DRM, you can use Calibre for managing (but not converting) the books, people can either borrow kindle devices loaded with the entire library (or part of it), or load books into Kindle apps.
2. Amazon support should be able to confirm that this works, and they'll be able to tell you how many devices/apps you can link to the same account
3. It might work with other DRM/Reader combinations as well, you'd have to check with the vendors
4. In my experience, Kindles (possibly eReaders in general) are great for reading books front to end, but don't work well with technical books - flipping backwards and forwards to re-read definitions etc is lousy, diagrams and drawings don't look great.