I've run Microsoft Security Essentials for the last 4 or 5 years without a virus-related issue - that was based on Todd's (tkam's) advice.
If you just need to read pdf's why wouldn't you just use Adobe's own free reader? If you need a pdf editing or markup suite I have no clue if any of the free/low-cost options are any good. I run the full version of Acrobat at work and at home.
No clue on the third item, I'm programming/coding illiterate.