Can I restore downloaded paid apps after a factory reset?
Once bought, always yours. New device, factory-reset, does not matter -- as long as your account stays the same. Paid apps are bound to the Google-Account you've purchased them with.

To give some proof: I use several apps I bought once on 3 devices simultaneously. I never was asked to pay again when installing them on the next device. Provided I used the same account, of course.