The classes you get offered GM rewards for are primarily based upon those same classes you ranked up during the previous leve timer. The more classes you are working on the more GM rewards for those same classes you will be offered during the next timer. Try ranking up just a single class during a leve timer to reduce the GM reward offers.

Ideally SE should always provide players the option of a gil reward in my opinion.

The battle leve ranks you are offered are based on your Physical level. So someone with a physical level of 50 will be able to see the battle leves for all ranks no matter how low thier highest battle class is. Ex. at physical level 20, you will start seeing the R30 battle leves, at level 30, you will see the R40 battle leves and so on. This also applies to the Gathering leves.