DS will do 4 A levels and that is the norm at his selective independent. Occasionally boys drop the 4th but that's very rare.
The range of subjects is quite standard so boys who want to do something non traditional tend to go elsewhere.
8/9 typically required to do the A level - 9 for FM.
I'd second the ask to be non judgmental about 'other' types of schools. I hate the threads that turn into state v private arguments. When it comes down to it we'll all parents who are doing the best to support our DC and trying to support each other.