I personally would not reuse floss. Germs and different bacteria can reside in your mouth and even with rinsing the bacteria may not be gone. I would suggest just using a new piece.
I'd say so. I'd also consider investing in a water pick. I got one for Christmas and it has been super helpful and I use it everyday, twice a day. You need to find whatever works best for your teeth.
I think that when it comes to floss it is very important to stay clean and part of that is to making sure you throw it away when done using! It's ok if you've reused floss before, but remember your getting out food that has been stuck in your teeth. Just keep your hygiene goals in mind and you should be good. I hope this helped!