Recovery from a cycling mishap
I recommend you take the bike to a bike shop and let them deal with this.


Yes, you can get individual spokes, but they need to be exactly the right length, which is determined by the specific hub and rim you've got, and the lacing pattern.
You probably do not need to rebuild the wheel with all-new spokes, but if you do, it will probably be cheaper to buy a readymade wheel.
Lacing spokes and truing wheels is not exactly a black art, but it is an art about which entire books have been written. You'd also need a freewheel-removal tool to get at the drive-side hub flange.
I'm a bit concerned that the spoke nipples damaged the rim at the spoke holes where they pulled through. And it is possible that there are other problems that only an experienced eye will be able to spot.
It's possible the derailleur hanger is bent.
Your new derailleur will need to be compatible with your shifters and your freewheel. I'm guessing that will limit you to a Shimano Tourney.