I really like the idea of using what you can, throwing out what you don't need. I've been working on a one shot lately using a Goodman games module, possibly adding a few other adventures as it goes. Also the idea of letting your players help world build is great. I started writing up a players guide and then decided against it. I'll let it come out naturally.
An example is that I'd like to have demi God's rather than actual Gods in the setting. Rather come up with silly names I'm just going to say there are 9 demi God's. Let the players fill in the blanks. Especially since this is a one shot, theres no point getting into way to much background info. That said, my gm brain is thinking long term just in case!
Should be fun!