The gutters are functional but he is trying to sell you new ones for aesthetics… he is a business man after all. The charge is ‘hefty’… … by your standards or you have compared prices with other gutter resources?
The vent should vent out the roof or the side of the home. Venting into the attic is against most codes. It can cause condensation during winter when it’s cooler outside, steam hits the roof and there you go. Don’t fault the roofer for following best practices, code, etc.
If the roof vent leaks, it should be warrantied. If you get mold, it’s on you.