Calculator [Q] At&t Samsung Galaxy S4 sgh-i337 mfc 4.2.2 [Where do I go from here?]

Hi, okay, so I've had my phone rooted for awhile.
I have a At&t Samsung Galaxy S4 sgh-i337mf3.
I've been using a minimalist rom given by someone on xda.
I love it, but now I'm thinking, is there something better.
  1. 1. Can I flash roms above 4.2.2 (i.e. 4.3, 4.4.2)
  2. 2. Would I have to update my phone using some odd technique?
  3. 3. What technique would you recommend for my build?
  4. 4. What rom would you recommend for my build?

Any help would be appreciated.