i have bettas for long time and i have 2.5 gall and 5 gall tanks. And for 2.5-4 gall tank filters are not necessities. A lot of times less water movement is better for betta.
You can do 1-50 and 1-100% water changes a week and your betta will be happy.
Live plant quarantine first because they can carry diseases. Just put in the water NO CONDITIONER for a few weeks. Wisteria may die;sword and jave fern may survive.
The same with betta i would quarantine it first make sure it healthy so you not ending up disinfecting everything.
Shrimp - he might want to eat the shrimp.