What's the biggest brew you'll end up making (size and ABV)?? Depending on how much grain you'll need to mash will determine if the cooler is a good size or not. You'll be hard pressed to get 35# of grain in that cooler/mash tun with 1.25qt/#... Actually, depending on what you use for a screen/manifold in the mash tun, you'll probably not want to mash more than ~34# in it... If that's enough grain for what you'll be brewing, then go for it. If not, then look to get a larger cooler to convert...
Of course, you could just start with that cooler, then when you need a larger one, designate the old one as where you hold your mash wort, or hot water for sparging...