(aw, im a seasoned member?)
So, in terms of payment... that's totally up to the pair of you. you need to have a conversation about what youll both be able to do, the power you each have over the project, and the means by which youll get money.
if youre mainly planning on posting this project online, dont expect profits significant enough to split any time soon. thats a slow grind, and the first few years will likely be next to no profit.
lets say you were writing this for submission to an anthology or publishing house though - the publisher will have writer and artist rates, which are out of your hands. in that situation, id say youre both working for free until your submission gets accepted.
id say, if youre not getting paid, then youre working on a joint project - make sure you are co-credited with your writer, and that you have say in the creative process. this is a little hard due to the fact youll be adapting something theyve already written, but make sure you get sway in the adaptation process. you are the comic expert, you know what needs to be changed, what visuals will work. as co-creators, you should be equally invested and powerful in your project. you should get 50% of all profits made off the comic. maybe 40% given youre adapting their novel, but i wouldnt go lower than that.
also, dont take it up unless youre really feeling it.
if the writer wants to go down more of a 'i write and commission you to draw' route (which is fair), demand fair rates. how long does it take you to make a page? for every hour, charge about $10 (i say $10 bc thats the living wage where i live, the longer answer is charge the minimum wage + however much you think your craft is worth), and youll get a per-page rate. if they cant pay that, you could find ways to simplify your style to a quicker time and therefor cheaper rate. but if this is gonna be a commission process, rather than a co-creation process, do not accept the work for less than minimum wage. it needs to be worth your time.
that said, take all this with a grain of salt - im not a prolific collaborator myself, being a reclusive control freak. but imo, there needs to be either mutuality or money involved. ideally both.