There are a number of variables. First and foremost is what the owner gets for freight. If he is consistently getting NLM freight for 1.50 or less, you should want a higher percentage, a minimum per mile, or a flat rate across the board. I don't recommend the last, as it doesn't give many drivers an incentive to do anything more than an adequate job. More than likely, the 60/40 or 40/60 will go out the window, depending on what the truck grosses.
Secondly, does he want you to share in the fuel pay? To me, that depends on how often pay is, and how far after the invoices are sent that you'll be paid. IMO, it's in the best interest of all involved for the owner to pay for fuel.
Third, do you share in the load-finding duties? IMO, if you do, you should get a bonus if you find one.
Finally, does the owner know what he's doing? That, you won't find out until you're actually working for him, unless you've already driven for a successful independent.
I pay my co-driver 20% of 80%, which comes out to 16% of the tariff. The 80% is what the truck would gross if leased on. The 20% off the top are the costs for doing business, such as insurance, load boards, and factoring. Also, I don't deal with FSC; so he comes out higher than a contracted driver who doesn't pay for fuel would normally get. I also set a minimum he'd receive if we took a cheaper load or LTL. His minimum is .25/loaded mi. On the bad side, we get nothing for relocating, and rarely get dh pay. Any accessorials the company gets, he gets 40% (again, 50% of 80%).
IMO, this is a great chance to learn the business from the inside. Definitely forget most of what you learned before, as it's useless here. You will be going from pressing a button on the qc to dealing with the brokers themselves. It can be more rewarding, both financially and mentally; but it is more work. Learn as much as you can. If you have a good mentor, you'll never go back to driving for traditional carriers. You'll consider doing so to be like going back to Algebra I after you've mastered Calculus.