I would use the cooler. I think you should maximize your output per brew session, and a 4 gallon pot will limit you , whereas a 10 gal cooler will not. As far as a pickup device, I personally use a slotted copper manifold in my cooler, but many people have great success with a ss braid. And as for step mashing,a) its possible in a cooler. B) you can mash in your boilpot first step(s), then transfer to the cooler, and(c) step mashings overrated IMO . You owe me two cents.