OP - sorry to hear of your mishaps. The tech talk has already been covered but think the best is to climb back on that steel horse and ride. For now, leave it one medium gear and screw fixing it. Just temporary. And for riding, keep the narrow (and replacements) on. Drop the seat a bit lower than what you properly should ride. Slowly ride some crushed limestone or pea-gravel paths or if not by you, hard to loose dirt / grass fields in a park. Take it slow and work your way to speed. Get loose, experiment like a kid
Beat it up a little... I mean in a good way. Do some rear brake exercises to near lock ups. Once you feel a sense of confidence, get on that road.
Seriously, I sometimes look for shortcuts and ride a 700 x 23C slicks on gravel paths and dirt roads. Fun and fast. Downhills are a rush. Takes a bit of confidence and thinking at speed but eventually you learn modulating both front and rear brakes to letting up, counter-steer works in harmony. You may not realize it but at high speed, counter steering comes naturally. If you think counter steer at high speed, you'll be flying thru corners. Now if I'm on a descent, asphalt surface and see a patch of dust or loose gravel, I relax and think of the line, straighten out and let up on the brakes.... ride thru it until you feel the grip again on the asphalt. Try this with heavily loaded touring bikes and you'll feel like your riding a bike made with pasta noodles! Then it gets a bit scary.