I have past experience in this market. My advice is to not do it, At least, Not with wow. The market is packed, it's viciously competitive and the profits are slim to none anymore. In order to do well, you must scale ridiculously high, for which there is a reason china owns the majority of this market. If you just want some spare pocket change every month sure set up a single bot and farm (or sell mythic runs etc). Otherwise, it's not the empire you think it is.. Not anymore
I do have some advice on where to look though. New MMO's that come out. Amazon's New world mmo has been spectacular in the closed alpha for which i am apart, And with Amazon's lack of experience in the mmo market, it's going to be prime for this sort of thing. There are a lot of other mmo's coming out or have released recently that you should look into as well.
Edit: I forgot an entire niche you could potentially look into and that is wow private servers such as ascension wow. These are locked down very tight though so are tough. This could potentially reach out to other game private servers as well.