Hey! Artist who files taxes and runs a business here here! Gonna respond to your questions individually...
(Also, I'm gonna assume you're in the United States? This is all based off my experience as an artist paying taxes and doing business in the USA.)
On average, how much do writers on here pay for artists? I ask this because I don't know how much I should pay an artist if I were to "hire" an artist. And what do you pay based on? (pages?)
This depends on the artist, but what @Kaydreamer put in their reply is a good start. Remember, making comics isn't easy, nor is it cheap! Folks put a lot of hours into making stuff, and even a black and white comic requires a lot of set up, determination, and skill. Plus, you should ideally be paying the artist time that they spend working with you on the comic, translating it into thumbnails, and generally responding to e-mails and giving you their time.
Regardless; some folks are looking to get their foot in the door and will do comics for very, very underpriced. Try to be nice to your artist and tip them extra if they do this. I can't control what folks charge and why (I used to underprice myself like WILD) so all I can advise is that you be kind to your artist! Talk with them and try to find something that feels fair.
Should I pay an artist based on their coloring (i.e. if they do B&W or colored pages)? The pages or panels they can complete per hour? Their drawing skill? Or do you "total" everything an artist does for an episode instead of focusing on one trait? (sorry if this question doesn't make sense...)
Ideally, you're gonna keep in mind the total amount of work and hours they put in. Color should ALWAYS be more expensive than black and white, especially if it's shaded. If you wanna split up your artists work load though, you could hire them a colorist! This could get the comic done faster too. So, really, it's all about time and what the artist tells you is okay, like a lot of my last reply went over.
Once you've accepted or "hired" an artist, what legal things or documents must you complete, if any?
Ideally, you two should both sign a contract going over who owns the rights to what, and for how long. So, are you wanting to own the rights to their art? Are you wanting to sell their art in a book? If so, they need compensation for that, and they need to agree to it beforehand. Are you gonna pay them upfront, or royalties after? Please make sure you decide this and sign something! The internet is full of template contracts for stuff like this, just do a bit of Googling.
So, my current idea is paying an artist $100 per episode (may be subjected to change), and my project is long-term. That means, as of 2021, the artist can possibly receive a minimum of $1200 a year, which is immensely less than the minimum gift tax in the US of $15,000. Therefore, to my understanding, neither I nor the artist will be subjected to any tax-related problems, correct?
See, the problem is here, you're not "gifting" the artist anything, you're paying them for a service. If you claim it as a gift, and get caught (this thread could make that VERY easy btw) you WILL MAY BE AUDITED. IT'S NO JOKE, PLEASE, I've been audited, IT SUCKS. Avoid it at all costs!
You and the artist both may need to sign and turn in the W-9, just so you know. BUT, W-9s only need to be signed if you pay someone over $600 in a tax year (from my understanding, please look this info up online and fact check everything I say for yourself) so if you only get a few episodes in a year, you won't need to file any special taxes outside of your regular taxes.
My advice is to get someone to help you with tax stuff if you plan to do this long term and for profit, it's really helpful.
If I collab with an artist, and we share earnings/receiving from alternative sources (Ad Revenue, patreons, etc), how does that play into taxes?
Anything you earn affects how much in taxes you pay. But, do keep in mind that paying your artist will count as a write-off for you. (It won't for the artist though, of course.) Also, please keep in mind that ad money pays BARELY anything on Tapas and Webtoons, and a Patreon does better with someone established. Do not expect to be making money off this out of the bat! Keep your expectations humble. My other piece of advice is to try and do a smaller comic with an artist first and see how you like it and if you can keep up with payments. Starting small to dip your toes in never hurt anyone-- it's always good to start small!
Good luck!