Can I set Commerce to accept floats for quantity rather than just integers?
Drupal Commerce supports decimal quantities, there just isn't a UI based configuration mechanism for using that vs. integer quantities. You have to alter the Add to Cart form and Shopping Cart form to change the #datatype property on quantity text fields to 'decimal' (or whatever you prefer) and then add appropriate validate handlers to ensure valid decimal values are being submitted. Search the code for datatype and you'll see the integer example code.