I'd really like for light usage to be free, but I'm undecided as to the best monetization strategy.

One option is for model creators to be paid when users download their public models.

The most profitable route would be aiming for a sharing platform, getting early stage investment, build a userbase, then sell the company. Both Facebook and Google are eyeing this field.

It's not even clear if this is more risky than a paid model, because the internet landscape is littered with corpses of paid-model web applications which didn't take off "enough".