Hey, I'll try my best to answer some of these, I completed 4 A-Levels last year at school and now doing 1 more in my gap year as a private candidate.
1.) You don't need GCSE's to sit A-Levels, although they may be needed for specific uni courses if you were thinking about this.
2.) The exam board doesn't matter, they are all equivalent.
3.) Some exam boards have more online resources than others, I found AQA to have the most online resources for Chemistry, so i took my a-level with them.
4.) I've not heard of a-level exams being in November before, is this possible? To answer the question, that seems ambitious but not impossible.
5.) Make sure you look into what you actually want to do before picking those subjects, do what you need, and nothing extra as in most cases it wont help you. For example, 99% of UK uni courses won't pick you over someone for having 4 vs 3 A-levels.