Do NOT have anymore contact with the buyer.
Do NOT delete his emails, put them in a file for later if he does take you to court(very small chance he will) to demonstrate buyer's remorse and his bullshit cost of repairs claims. He bought a used vehicle as-is, there is NO WARRANTY.
Report the plates to the Police and/or DMV immediately
Enjoy the new truck you bought.
Buyer is a bullshit artist and is used to doing shit like this. It makes me wonder how many he has actually scammed in the past.
From a shop owners perspective:
Any mobile window company that does windshields will remove that rear glass and re-seal it for $200 - $300 as long as the frame is not rusted out.
The reverse lights repair, other than bulbs, is either a switch, bad sockets, or wiring. 2 to 3 hours(max) of labor plus parts. $200 to $400 tops.
Fuck that guy, and move on. I believe he is all talk and intimidation.