SloJoCro said:
It's not a “breach” for him to demand payment upfront though.
Refusing to work is a clear breach, though. You can't apply for a job at - for example - a restaurant and then demand to be paid for two months upfront. It doesn't matter whether it's in the contract or not because the law automatically is part of the contract.
SloJoCro said:
If you're going to do a fixed-price agreement like this, you need to be careful not just about when the payment is due but also what he actually needs to do to trigger the obligation. You don't want to be stuck paying him if he delivers complete crap. It seems like you used an agreement template that wasn't suited for fixed-price.
The contract does specify the scope of the work, i.e. which models need to be made.