[Solmu]

Should I attempt to sell the designs to large apparel companies (perhaps on a commission basis) as a freelancer at this "start-up" stage (I don't even know if they are open to that or not), or brave the waters as a tiny fish?

You'll probably get biased answers here since most of us are running (or trying to run) our own business. Personally I'd say brave the waters (and consequently make more money if you're successful/have more creative control, etc.). If you find it's taking too much time away from other things you can look into other options then.