I don't know how to bring this up without sounding disrespectful, but why take a job at CommutAir if you're already wondering how to go above guarantee? You'll be making less than $1800 a month until you upgrade. Even if you pick up 10 hours of OT a month, you'll barely break $2000.
I understand the quick upgrade, etc. But I wouldn't consider working more hours at that low pay. Just hang tight until then.