I worked pretty much alone on the code base for the first three months. Then we were two people for another three-ish months. Then the last four months or so we've ramped up the team to have 4-6 programmers on, depending.

But we're also ruthless about keeping the code base small. In the beginning I would go through the entire code base every week and prune it. I still read through the entire thing every now and then and make sure there's no excess fat.