Mr. Softie's tummy has been bothering him again and I can't get him to the vet anytime soon. Every couple of days he throws up stomach acid and his poops are very runny. If any other hexbear out there has experience with a cat like this, is there any food you recommend?
Do you do it outside or under grow lights?
If you want it to live for longer yeah, wheatgrass needs full sun. You'll need a decent powered grow light to keep it going indoors as it's pretty sun hungry. If you just keep cycling new planters/pots, the wheatgrass seeds have pretty much everything they need to stay alive for fairly long, at least a month.
There is a number of issues with keeping it going, wheatgrass will eventually start growing more of a stalk from the bottom which is less desirable to your cat. You asked will need to feed it something heavy in nitrogen. Wheatgrass tends to come in a winter and summer variety as well, and I'm unsure what that means for long term growth. It's honestly a fairly finicky grass to keep alive.