In as much as I can:
1: I have no idea, I raised it with the PoC at HQAC when it was first developed and I never did understand it.
2. Nowhere, it falls outside most other areas, it doesn’t count as trekking, so you don’t officially need BEL or higher, you definitely need First Aid quals. The only real ‘qualification’ is attending the First Time Team Leader’s weekend with RAF WARMA, but I didn’t get a lot of value out of it tbh, (And I think I got more than most, it snowed really heavily the year I did it and day two was called off, so we sat in a conference centre at Cosford and actually talked about Nijmegen and team leading, which didn’t seem to be on the agenda otherwise?)
4: 1:10 realistically. But I wouldn’t recommend it. Two of us took 20 cadets to Nijmegen last time I went, and it was a struggle. (Especially when we all got tired, cadets and staff)