Welcome to the hobby OM. You came to the right place for advice. Most of your questions have been answered but here's an opinion from an old-timer who remembers crystal controlled 2m radios that put out only a few watts 50 years ago hihi.
As far as power output, most new radios have selectable low/medium/high power outputs and you can pick and choose what power level you want. Higher power will definitely increase your range, both on simplex and for accessing distant repeaters.
The question about which of the two bands is more populated all depends on location. You can go to the ham radio database here on RadioReference to see how many VHF and UHF repeaters are in your area just to get an idea. Best way is to just listen in for a while and determine for yourself. Here in Western NJ, UHF appears to be slightly more active, especially during commuter hours. During the day though both bands are quiet.
If you can, avoid those cheap Chinese imports and pay more for a well made Japanese radio from Icom, Alinco, Kenwood or Yaesu. Their manuals are well written and they are much more reliable.
If you choose to go the used radio route, either now or in the future, realize that there are many older units for sale which could save you some money and that is fine, but many of the older units have internal memory batteries that have a limited lifespan. If you buy one with a dead battery, it won't hold memory and you'll need to replace it. It can be easy or very difficult to replace. I've done many replacements; some were easy, others required delicate surgery as the batts were soldered to a board.
When shopping for a radio, look around to see who offers free shipping. Most do though.
Well, enjoy the radio hobby!