7" x 13" is a pretty wide plate, I don't think 3 power tabs is overkill. At the worst, it won't hurt to have extra tabs.
I've used 4 tabs before for 7" x 7". That probably was overkill, but it didn't hurt production.
Those that have tested the various "paint on" methods for insulating edges, reported that nearly everything lifted off the SS after moderate running time. Even weldon-16 (or equivalent) has trouble sticking if the plate surface isn't media blasted first.
I bought "liquid electrical tape" with the intention of using that on the edges .... before I read those negative results.
At least I had something to paint over the external connections.