Genre is key! I think writers with limits often relate to pretty broad categories. (Can they write comedy? Horror? For children? Are they comfortable writing a sex scene?) There's both skill limits (I am not a pure comedy writer) and personal limits/preferences (I am not comfortable writing evangelical projects)
An episode a week is 100% doable. Writers often have word count based pay, but that gets trickier on comic scripts since you could pretty easily bloat description to get more pay.
I think a lot of writers, me included, are over the moon for the chance to write for pay. Heck, a lot of writer's jobs involve working on somebody else's IP. Superhero comics, ghostwriting, TV writer's rooms, etc. I'd recommend
-Having a contract where they have a script ready every week on X day, you have edits back by X day, and they make changes by X day, maybe 2 weeks behind the art.
-Development meetings. They can pitch ideas, ask about issues, and point out concept problems you're having.
-Ask for a writing sample, and a script sample if you can.
-Remember you can ask for specific types of scripting. You want to make sure the writer understands how to pace action for comics and communicate motion. More detail, less detail, if you want notes on paneling, etc.
-If you can pay professional wages up front, you don't need to offer royalties, but, the lower the pay, the more I'd recommend also offering a percent of profit.
When you're willing to pay, you're the boss, so you get to call the shots. The biggest thing I'd be careful of is making sure you're on the same page about the 'final say' issues. The more you can be on the same page up front, the less you have a frustrated writer doing the same scene five times for no additional pay. (But you also don't want to pay extra for changes and incentivize mistakes)
