I believe bitcoin asks 10 nodes for block data: 8 "regular" peers and 2 "blocks only" peers. It thus has an implicit trust assumption that at least one of them will provide data for your node to validate. I suspect the same N can be used in this protocol without any change in the trust assumptions: your only expectation is that one of your peers will provide the data (the proof) if it exists, and you then validate the proof yourself.