1) I fly 10 flights BA F.
2) I pay for about 8 of them, I always buy fully restricted tickets however, as I can't justify to myself paying £14,000 to Aukland, only to change my mind over a couple of extra days.
3) I take zero F flights for business.
4)I pay for about 80%, I tend to use my miles to upgrade my CE trips or use for Business class trips as it's a better use of miles.
Hope this helps