Lots of good info so far. You'll get used to the new riding position after a bit and it will be more comfortable. Yes, the '03-05 Gen I bikes put out a bit more heat than the '06-on Gen II bikes. Many don't find it an issue, but you're in a warmer environment too. Don't be afraid of higher mileage bikes, the motors last easily to 200k if no bad shop techs interfere.
The glove box latch pretty much means replacing the entire unit for about $120 or making up a new lid/hinge and latch. Several people just did some Home Depot fab work and a simple cabinet latch instead of paying for a new factory unit. Some of them look like it sounds, some look really clean too.
I have an '04 w/o any heat fixes, but live in a cooler location. I've ridden all over, and spend full days in high heat on many occaions w/o noticing the heat. A cross wind can cook one leg though! It's an individual preference. The heat fixes are pretty easy to do and do make a difference, but not as much as a Gen II, imho. Try to get a comparable ride on a Gen II just so you can see for yourself, even if they are out of your price range.
I too had some numbness issues. The Gen I needed some handlebar angle changes to solve that issue for me. Some Heli-risers did the trick, though I really didn't need the rise, just the angle changes.
Lenkadapters offer minimal rise, but a nice amount of angle adjustment. Check out the full offerings from
Wild Hair Accessories. A radiator guard of some kind is a really good thing™.
Now days I consider a throttle lock of some kind and a Throttle Rocker or Cramp Buster to be mandatory kit. It allows you to relax your hand and use your palm to control the throttle position. The throttle lock gives you a chance to shake out or just do other things with the right hand now and then. Full on cruise control is nice now and then, but not really something I need most rides.