Personally would go19x22 for fabric. Gives you little more than 3 inches per side for framing. Needle size 26. Anybody want to double check me? Please do. Lovely pattern.
PS: since this is a coverall pattern would start from upper left instead of traditional center. Just remember to start 3 inches in from left side if material and 3 inches down from top so you have your framing border. Happy stitching and post progress pics please.