Hey Red Roof. Ideal would depend on the system you want to set up. I BIAB so I have no coolers and the only thing I needed to go AG was a bag but from what I gather if you do use a cooler it's sufficient to have one to mash in the lauter over into your boil kettle. Good luck!
I got a 20 gallon cooler I do 5 and 10 gallon batches in, I only use 1 but I have 2 kettles. You could get away with 1 kettle, or even just brew in a bag like lots of people do.