I use either the 3 or 5 gallon auto pot fabric bags. I prefer the 3 g bags, less coco needed and the 3 gal in coco is enough media to grow a big plant.
For extras a valve for each pot so you can turn off individual pots. A valve at the exit of the res so you can do maintenance. And I use the air bases in the bottoms instead of chunky perlite or hydroton.
The kit will have everything you need. You dont need an extra base. My suggestion was for some extra valves for your set up. I also bought the air bases for the pots, not needed if you line your bag with hydroton, I like the bases and they are re usable. Your kit comes with 2 valves, I would order 2 more.