Buy the best you can afford once, save money in the end. I bought the 10 gallon Polarware to start. Pricey, too small, now is my hopback. Bought a 25 gallon Mega Pot and love it. Bought from a commercial restaurant supply for $200. I would go 15 gallons at a minimum IMO. I brew Natural Gas outdoors. This and the stainless MT for me is out. I couldn't imagine fighting temps during a winter mash. I have almost no variant in temps for 90 minutes. That is a plus for me on the cooler. Mine is 120qt Igloo MaxCold and I really like it. Coolers are cheap, easy to build, and work. You can get by with a little smaller HLT to begin with. Heat your strike water in the lager boil kettle, and use something cost effective for your hot liquor tank. I used another cooler I had for my original HLT. You don't need flash and bling to make good beer.
Gas vs electric is a huge difference. I think I would have to start with gas. Down the road, if your still brewing, then think electric. Give yourself some time to learn what you like, don't like, then you will figure it out. Everyone here has adapted their system for their setting, and what they like. You will end up doing that too. My vote would be nice large BK, cooler MT (70qt-ish), reasonable HLT, and a gas burner. Good Luck!