1) I didn't do foundation science so I don't really know but it is likely to be easier than higher, but it probably won't be 'easy'
2) The pass rate for people with rest breaks I do not think is specifically recorded so it is impossible to know. I didn't get rest breaks at GCSE but I have them at A-level and I am currently on track to get AAB or ABB, so I wouldn't worry about it.
3) If you fail one science you do not usually have to resit it.