Last year, someone got accepted with these stats (found from the senior physics challenge 2021 thread), 250 C1, 145 C2, 32 C3, 29 FC1, 4 FC2 and 10 Uni C1, and he did a total of 220 c2 and c3 questions (and above), so I think 400 c2 and c3 is a bit excessive if you just want to make the summer camp. But obviously, the more you do the better.