Hey man, I know you probably have the best of intentions, but this is straight up a bad deal.
If you have the financial security to drop your job and only rely on Kickstarters for your income, great (though boy howdy I would lower your expectations). You might even be able to find an artist that is lax enough to take that payment cycle and do it on the side. If they're okay with that, cool.
However, you are asking way too much from someone who is going to get paid like, twice a year, and it's a BIG IF because it's a Kickstarter.
25 panels a week? That's insane. That's the equivalent of 3-4 normal pages a week. which is what a normal, able bodied full time comic artist might do. Because you're not paying them right away, this person is going to have to keep their full time job, or they're going to be at school, or have other more important life obligations. Most webcomic artists do 1 page a week, which is maybe 6-8 panels. Even stretching that expectation to every two weeks is too much for the average hobbyist, and frankly since they're not getting paid during it, you're going to have to deal with them prioritizing other life dealings over you.
You literally admit that you have had issues keeping artists on retainer in the past due to this exact issue. Promising Kickstarter funds isn't going to solve this problem. You're still going to get the same types of people who can't commit because you're not giving them enough in return for their time.
What you should do is keep your job, put away the money in a savings, pay the artist as you go, then do a Kickstarter to recoup that money. That way if it fails, the failure is on your shoulders and not the poor artist you hired.
Or hell, pay the artist for Kickstarter samples, do the Kickstarter, then use the earnings if it succeeds to pay them while they produce the rest.
If you're set on your current model, lower your expectations significantly and be prepared to pick up the slack. Maybe ask for 6-8 panels and flat color while you do the scripting, thumbnailing, lettering, and effects. This is a give and take here.
There are plenty of other ethical ways to go about this. Please consider any of the above options. You can have all the confidence in the world, all the technical skill, all the connections, and still flop. It's fine to fail, but it's not fine to risk dragging someone down with you. As a creative manager, if you've got to hire someone, it is your duty to make sure they are taken care of before you are.
