JD:
I'm in the planning and gathering stages of an all electric 2 keggle system myself. Up front, three safety practices to consider: GFCI circuit breakers for all power to the system, excessive grounding of everything, and positive isolation of 240 V heater elements if that's what you plan to use. Controlling one leg of a 240 circuit will open the circuit but still leave the other leg energized.
I will use an igloo cooler for my mash tun. I bought most of my control devices off eBay.
For my HLT I will use a Love PID controller with a relay contactor and a thermocouple to control a 240V/4000W hot tub heater. I plan to put a motorized stirrer in it to eliminate temperature stratification. Can't post pics or plans, don't have them yet. Oh, I will also have a dpst 30A switch to positively shut off the current to the heating element. Thinking about having some sort of level switch in the system so I don't dry fire the heater element, but not clear on which one, or how.
For my boil kettle, I plan on using a 240V/4500W ultralow watt density water heater element, controlled by a PWM dc motor controller to fire a solid state contactor and not a PID controller since I want 100% power to get to boiling then want a simple way to dial it back to less than 100% for a steady boil. Will also use a 30A dpst switch to isolate the element in a positive fashion.
There is a lot of good expertise and advice on this and other brew forums, do a search on any of them, and google for things like "electric hlt" or electric bk", etc. Most of what I have summarized here I have learned from others who have done this first, although I might be first to use spa heaters, don't really know, haven't seen any mention of them yet.
Good luck, keep us posted on your progress.