Thanks for the ideas and comments!
I have looked at the Bayou, and Polaraware stuff and agree they seem too thin to get a good weld that will be structurally sound. Have also seen bad reviews that complain about inconsistent wall thickness, un-passivated surfaces that start rusting, etc.
Still looking at restaurant supply sources, but there is a substantial difference in cost for the thicker solid bottom pots, as I was expecting, but it's quite a steep curve to say the least. I will probably stick with keggles for the time being, at least they weld up fairly easy. Luckily I have been a "hobby" welder for several years and have a decent tig machine that I have used for SS (304/316/409).
I have tried the silver soldering method as well with great results. It's an excellent way to go if you don't have access to adequate equipment, and experience in welding.
My plan for the electric heating elements for the boil kettle are to make them vertical, but contained in a calandria sort of setup. That will allow the concentrated heat inside the cylinder to pull wort from the bottom through open ports and with convection push it up to open ports on the top of the cylinder (sort of like a percolator). There will be three elements controlled by the PLC that will each have it's own PID loop, so as the demand decreases (as it gets closer to boiling) it will shut off one or two elements as necessary to keep just enough heat for a good rolling boil. Of course this is all R&D at this point and have no idea how the end result will pan out, or what the final configuration will be. But heck, half the fun is trying new ideas and spending countless hours tinkering with it.