Don't have much help in way of the first problem, but I would definitely recommend taking your bike to a local shop to get it tuned up. Most places will do it for cheap, and it can make a huge difference, even to an old bike Or, if there's nothing too major wrong with it, I could point you towards some materials to teach you how to fix it up yourself, which can be a really nice set of skills to have, and save you some money in the long run. As for running in the fall, I'm still at school, so I can run in the middle of the day when it isn't so cold out. It's definitely going to be harder once the temperature starts to drop more, though.
Here you go! http://www.sheldonbrown.com Ignore how ugly the site is, there is some great info on there. For me, what helped really understanding my bike was that I had to take it apart, ship it, and put it all back together for an internship. If you happen to have a junky old bike sitting around, or could borrow one from a friend, I would definitely recommend trying to take one apart completely to try and understand why everything does what it does.