I've been thinking about this, (not sure about the betselection)
3 numbers for 10 spins, then +1 bet
4 numbers for 8 spins, then +1 bet
5 numbers for 5 spins then +1 bet
6 numbers for 5 spins then +1 bet
7 numbers for 3 spins then +1 bet
8 numbers for 3 spins then +1 bet
9 numbers for 3 spins then +1 bet
10 numbers for 2 spins then +1 bet
11 numbers for 2 spins then +1 bet
12 numbers for 2 spins then +1 bet.....
Have you tried the coldest numbers? 1 number can sleep gor 600+ spins, but not several at once... Anyway, you will still lose . How often and how much you can make in between are the questions...