OLM is trusted. Maybe we could stick a £5 entry fee on, to the CTWD PayPal, and trust him to send it on to the winner? That'd be a £480 pot. £100 for the 3 winning numbers, £50 each for the 3 runners up, £10 each for the 3 third place.
I know you said "I'll wait until all numbers have 3 names next to them", but I think you should probably change that to 2 names. Might take a while to get 3 on all of them. 64 people at most sounds enough, even then maybe too many. If I were you i'd stop when you have all 32 numbers taken now.
That pace is not going to keep up. Having 3 people per number means you'll have 96 names. To me, that seems like too many. Also - expect the numbers to drop massively once the initial 32 numbers are gone - people will think the sweepstake is full and ergo will not join in.