Yep, definitely need 256GB for comics. Heck, if Apple releases a 512GB model, I'd probably get that one as long as it's not cost-prohibitive. I think a single 20-page HD issue on Comixology uses around 50MB and is good for maybe 5 minutes of entertainment.
Since I initially started reading because of manga (right to left pages), I use ComicGlass and have continued using it for DRM-free comics (e.g. Image, IDW, Valiant, etc).
I've got a subscription to Marvel Unlimited so that app's mandatory. For Marvel stuff not on Unlimited, I use Comixology. Typically, I just wait for sales on back issues/collections but for ongoing series I'm currently following, I pre-order floppies from Previews/LCS at 30% off cover and use the Bonus Digital Edition code. DC, I get from Comixology, too, when they're on sale.
Honestly, I'm more of a DC gal (mostly due to growing up watching 90s Batman, Superman and Justice League cartoons plus Christopher Reeve Superman and Michael Keaton Batman). However, I find myself reading and buying a lot more Marvel comics due to the existence of Marvel Unlimited (e.g. read something on MU and if I really like it, I end up buying physical HC or TPB edition).