For a five gallon batch, it will be too small given what you will need to start with to account for evaporation. You could either do smaller batches, partial mashes, or mash to achieve a higher gravity and continue to top off.
I would recommend a 40quart minimum. I was recently in the same situation and got the 32 quart and i wish i got bigger (ive since gotten a 15 gallon). For a 5 gallon batch you want to be boiling 6.5 - 7.5 gallons depending on your boiloff rate. If your pot is too small you will be constantly tending to boilovers.