Are looking to stock with fish only? If so, then like the user above suggested, with 3-5 gallons a betta would be nice. Also one dwarf puffer is another option! Maybe endlers or a small shoal of microrasboras like chili rasbora? If you can though, I’d go for the 5 gallon instead of the 3 gallon because the extra 2 gallons helps widen your choices a bit more! Plus extra space for your fish is always super nice 🙂
You could search up some plants that do well without added fertilizers/dirted substrate as I’m not entirely familiar but I hear mosses, java fern, anubias, hornwort and wisteria do well with just necessary trace elements from fish waste and water changes.
Are you planning to set up the tank before you move into the dorms or after?