It's been quite a few years since I last brewed, and the memories may have faded somewhat. I had a heated polybucket (Electrim, but nowhere near as sophisticated as their current model), which served as both mash tun and boiler. The malt was held in a deep cylindrical bag with strong sailcloth(?) sides and a mesh bottom, with cord loops at the top so it could be held firmly in place with a strap round the outside of the bucket. This kept the malt from contacting the heating element and scorching. When mashing was complete, the wort was strained off into another 5 gal container. If I started brewing again, I'd probably do the mash in my large Coleman extreme coolbox, to save both time and electricity.
Sparging is crucial to getting the maximum extract; I used to sprinkle hot water from a kettle as evenly as possible, but a modified watering can might be better. I then had to remove the malt bag, clean the Electrim, return the wort and start the boil, bypassing the thermostat to prevent it from interrupting the boiling. Like you, I had a home made cooler, made from a coil of 8mm copper pipe.
Your suggested setup sounds more efficient than mine was. If you use loose hops, you'll need a hop filter to stop them clogging your tap; the malt bag can do this job at a pinch. Will you fit a heating element to your mash tun, or will it be well enough insulated to keep the temp within a couple of degrees of optimum? Why two elements in the boiler? A single 2.4kw kettle element should be enough, I reckon. How wide is the neck on your wine fermenter? If you need to jiggle the false bottom through the opening, getting the spent grain out might take a while!
