Mark, not sure you mean insulate the sill plates, but rather seal them to the top of the foundation to stop air infiltration. A good flexible caulk no need to be 100% silicon, very expensive when there are DAP products out there that will do a great job for you. I would consider first insulating the band joist (is sits on top of the sill)all the way basement. If budget allows i would use 1" to 2" of closed cell foam insulation. If not you could do it yourself with R-30 fiberglass cut to fit between the joist and please put a couple of staples in it so it doesn't fall out! After that i would tackle the walls
