I'm trying to figure this wiring stuff out myself so take my advice with a grain of salt.
I don't think you need more than one pid. You also don't have to have a temp sensor in the boil kettle. You simply need one to be hooked up somewhere (and it will be - in the rims tube). You then run the pid in manual mode to power the element in the kettle.
That said, having a sensor in the kettle is nice because it will help you anticipate the boil and track progress during chilling. That's what I plan to do anyhow.
There is a great diagram by P-J that I'm following that should also work for you. Do a search for "simple eherms diagram" and you should find it.
As for SSRs I'm not sure you need more than two. You might be able to get by with a dpdt switch to switch between the elements. Three SSRs would work too.. But would be more expensive.
Lastly, it's probably not the best idea to be drawing current from multiple sources. More wires to trip over and more stuff to unplug or switch off in the event of a SHTF moment. I'm 240v single outlet and wiring doesn't look to be too bad but I do have the breaker box located mere feet from my rig. I would at least consider putting in a single 120v gfci outlet on a breaker that will handle your amp requirements.
Again, caveat emptor. What I know I've read or been told by the experts like Walker, PassedPawn, P-J etc. hopefully one of those guys can chime in with more useful advice.
Edited: forgot you have 2 elements in the boil kettle, that changes things. Still though, two SSRs should work since you'll only be running two elements at a time. Then you switch off one SSR and switch the current from the other one to the rims tube. I think...