sounds like you had a great time! i know some of my favorite rides have been through rain and snow. 50 miles is a pretty decent ride, did you have to do a lot of climbs or was it mostly flat?
500 bones will get you a very nice used bike on craigslist. why buy something less that's new when you could pick up a high end bike that's only a couple years old on CL?
I have full XT on my cross bike, but keep in mind that you will run into compatibility issues if you use road shifters with mountain derailures. For example, a front road shifter does not pull enough cable with each click to shift your front derailure. You can fix this but it's not easy. Then...
like some others have said, focus on lifting the pedal with your front foot rather than pushing down with your back. for me, it was an 'ah ha' moment when i stopped trying to force my back foot down to skid
if you're commuting, then i recommend inspecting the tires every once in a while and pick out all the glass with the tip of a knife. most flats happen because glass and other road debris work their way through the tire over time. you'll be surprised how much junk you find hidden in your tires...