What kind of banners are you specifically looking for? Text only, or using toris and stock images in your work?
Depends on event - some would be fine with simple text banner or even without - like 'Guess the Staff member', others like f.ex. Sir-caps-a-lot, needs something a bit better.
Also, how often is an artist to make a banner? I'm already in school, so I'm not always active during the week.
And again - depends. Don't take my words as a fact, but let's say we host 4 events each month and something bigger (like Vampires vs Zombies) which would need a lot more work every few months. Let it be 4 banners a month, for now. Sometimes less, sometimes more.
Does this include editing?
If you mean video editing - erth already answered that question.
Will there be any form of compensation in return for your use of our artistic talents?
If not, what incentive is there for us?
As first post says - this job is unpaid.
Gamemasters do not receive anything as a payment for their duties as well.
You might say that we have ~ and some other 'cool stuff'. That's correct, but as an artist you won't need them.
Title of 'Official GM's Artist' surely will bring you some fame and respect, but that's it.
Side note: As it says in first post - we might be taking few of you, so you shouldn't worry about being exploited.