1- You could use a USB stick yourself as a extra layer of security IF you prefer. It's not required however.
2- VAC bans + Overwatch bans effect the account that the cheat is used. Your main will be safe.
3- Even if you did it still won't be a issue. (Yeah they won't be linked)
1- Waay too long ago. When it was first released, been years at this point.
2- Bank transfers might take a while. Stripe is instant.
Do let us know if you have any other questions.