There are lots of mods out there, you'll want one that fits a 24mm tank though without overhang. Maybe a smoant battlestar, charon, vaporesso revenger, voopoo drag, tesla wye. Some are boxy, some are contoured, some are trapezoid shaped like the battlestar/wye.
For premade coils you can buy either mass produced in various amounts either by a specific type like a pack of claptons or pack of aliens or you can get variety packs that have a few different coils. Demon killer coils have variety packs, places like advanced vape supply have packs of 10 coils for $7-10. Advanced vape also has handmade coils like aliens that sell for $13 a pair. That's the other option, nice quality handmade coils from folks like
@b_d_builders and I think
@raymo2u and
@whiteowl84 may sell them as well. Not certain on the last two, if they're actively selling to folks independently on a regular basis or not, they may have other projects going on. All 3 are members on the forum here. They can make you just about anything you want and may be able to make suggestions for what coils may work best depending on what sort of vape you prefer.
You'll also need cotton or wick material to wick the coils once you've installed them. I like muji japanese cotton pads personally. Some like rayon, some like cotton bacon v2 which I believe is a blend of cotton/rayon. Native wicks is another brand of vaping wick. Some like muji or koh gen do are sold as makeup or cosmetic pads and they're a square pad. You cut a piece off lengthwise and most people peel the outer 'skin' off both sides then roll and pull through the coil, clipping off the excess. Stuff like cotton bacon comes in a sort of long 'bunch' and you peel off what you need. Some even use cotton balls and unroll/unravel them.
It's worth searching around for wicking materials and wicking preferences, a whole page could be devoted to that alone. Between different materials, organic vs processed, bleached vs unbleached, whether or not to boil/wash prior to using. Even down to how to prepare it, simply rolling it into a wick, peeling outer layers of pads or not, feathering out the cotton first then rolling it (scottish wicking technique). Not trying to confuse you but there really are a lot of options and variations out there and may take some trial and error before deciding what you prefer the best. Beyond just screwing even a premade coil into the rta.
The nice thing with rta's though, if you screw up a bit of cotton or rayon or whatever you don't have to chuck the coil. Simply grab another piece and try again. Sometimes there's more optimal ways to wick just based on which atomizer you're using.
Not sure how new you are to vaping, you'll also want some decent batteries to go with the mod and an external charger. Lg hg2's, samsung 25r's or 30q's, sony vtc5a's would all be solid batteries. Some people like efest chargers, others like nitecore or xtar. I use an efest luc v6 and it's working well for me for what I need. I'm sure others will give you more suggestions for stuff to try.