It sounds like you're over complicating things.An 8 gallon pot should be (may be) fine for strike water and as a mash tun, as long as you're not doing anything too big. When you want to start doing the bigger beers, you're going to need some bigger equipment (at least for your mash tun). For instance, my recipe for Kolsch is a fairly small beer and it takes 8.25 lb of Pilsner and half a pound of Vienna for a 5 gallon batch. So for a 10 gallon batch, you're using 17.5 lbs of grain. Your mash would have 26 quarts (4.2 gallons) of water. This means your mash tun would be pretty full. And this is only a 5% beer!