Kat, it's up to you, but if you know you can do more than 10, I'd encourage you to start in group 3. I expect you'll progress quicker that way. The last set is always a max-out, whatever group, day or week; the first sets are building your base.

There's another exhaustion test after weeks 2, 4 and 5 where, if necessary, you can move into a different group.