For almost all flying you won't see any real benefit from more than 10% nitro.
Almost all general purpose fuel has close to 20% oil. It's worthwhile to have some castor in it. Synthetic does excellent stuff, but having some castor is a really good idea.

Try a gallon of 5% and the Omega has both oils in it's mix.

There aren't any magic fuels. And no magic amounts for nitro or oil. So almost any Byron's you get is going to work well. But don't waste money on specialty blends, like for heli's. And don't worry about getting more than say 10% nitro. 5-10% will run excellently well. But do look for a blend of oil. Castor isn't magic, but it is good to have in the mix, for a beginner.