Hi there and welcome to the org!
A 22 x 18" pot is typically 25 gallons, a good size for dwarf Cavendish. For soil I recommend Kellogg Garden Patio Mix available at Home Depot etc., or Sunshine Professional Mix #2 which you can obtain at an agricultural supply store. For fertilizer I recommend 20-5-30 water soluble, which you can buy directly from Grow More in Gardena or at my web site below.
