You definitely don't need a guide to have a great time. That isn't to say that people don't take them, but it depends on what matters most to you. I prefer to be out in nature, do a little fishing, hike a lot, and have fun with my wife or friends. None of that requires a guide. If you want the best, secretest spot, or if you just want to enjoy and not work too hard, a guide is a good choice. The fishing shops are generally quite good.
As far as accessibility, there is almost no private water in MT as far as fishing, so you have pretty much run of the place. It is rough country, though, so be prepared to work a bit. It's pretty limitless. There is plenty I want to do but still haven't done. A bunch of mountain lakes I'd like to fish, etc. But really it is all great.
Do be bear aware. This area of MT really does have a lot of grizzly. Obviously, you are not averse to guns, so have one with you, either a 10mm or a 357/44 mag. Also, have bear spray just in case. It's a gross motor skill, as opposed to shooting, and the bears are terrifying when you see them. For your wife as well, if you are traveling with one. Don't be overly concerned, but be smart.
