1) Well, you'll be in the mediterranean area, and all my November travel is limited to the UK area, but I'd check an online almanac for weather patterns at that time of year. But anytime of year, you can't go wrong with a basic set of clothes (shorts, jeans, long-sleeve and short-sleeved shirt) plus something for RAIN.
2) It's always cheaper to fly into London, it seems, and that's what I generally do. But getting a budget flight out of Heathrow to Spain is prettty tough. Usually there are only BA/Iberia flights that cost just as much as the price difference. If you're willing to get out to a satellite airport, you can hop on a budget flight, but if your itinerary doesn't include the UK or France at all, I wouldn't bother. then again, you're gonna be there a few months, and France DOES border all them other countries
3) Don't sweat it. Sure, the image of America isn't so shiny out in the world, but most people you meet also know that any American they'll meet abroad is a lot more open-minded and cool than the 80% who choose never to leave the country. I wear my "NOT MY PRESIDENT" shirt sometimes, but it's more of an icebreaker than a "don't pick on me" thing.