Well my good man I prefer kanthal on my RBA's and there are many tanks to choose from if you are looking for a good one you could try the Kanger mini tank or the Billow v2 here is the rip tripper review
I don't know if you into building but the billow is an RTA only by the looks of it, I would recommend the kanger mini tank for beginner builders.
Nickel coil builds are hard to do for the Istick TC40W.
But like I said I am a kanthal fan and a 26gauge at it.
if you go with the kanger mini subtank V2 you can still rock the occ coils! and it will sit nice on you mod!