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?
I would consider growing wheatgrass for your cat as well. It's very simple to grow, and sprouts very quickly. You don't even need to worry about feeding the grass either, you can just let the grass die off in a month-1.5 months and have another small planter going. The grass provides a lot of nutrients and fiber and it supposedly good for cats digestive health. Certainly in the wild cats are eating meat/organs and otherwise chewing on whatever plant material they find.
There's a possibility your cat doesn't respond well and if they barf up grass you can decide if it's not worth it. I guess you should also try to make sure your cat doesn't have worms (if they got fleas at any point that is the primary vector), because some worms can cause vomiting as well.
Personally my cat is obsessed with wheatgrass and if I don't grow it she will search out literally any house plant available to chew on.
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.