Don't bother with 5, it's not neccessary. Focus on what you want and spend the extra time from not doing a 5th subject on doing extra on your chosen 4.
Back to your original question, subjects seem good to me, nice and broad, but really it depends on where you see yourself going and how good you are at them as to whether they're good or not.
These are the subjects I did, except I just did english language (which was terrible). In my opinion they are great choices in some ways, especially if you want to do politics/economics at uni, but as many have said on here Further Maths would be a real strength if you wanted to apply for economics, (which, as a result I may end up sitting as AS-Level this year). Why not start out with 5 and then perhaps cut down to 4 depending on how you feel when doing them?
No, that'd be the stupidest decision ever. Most universities don't even count it as an A-level - they explicitly state "Excluding General Studies and Critical Thinking". Most people only do it because their school forces them to. It's not a proper A-level.
(I'm not saying it's easy by the way before someone starts flaming me, I actually have no clue what the content is really like. I just know it's very disrespected.)
hmm whether other people think they're good choices or not realy doesn't matter. What does matter is if you think they're good choices and if you think you'll enjoy them. You don't want to be sitting through a lesson that's boring you to death now. so just pick what suits you.