I just fixed up my basement on the cheap. Painted the cement walls harvest gold behr basement wall paint, threw down the cheapest rug off the roll from HD, so thin I cut it with scissors to get around the poles in the basement, went to wallmart and bought tan tab top curtains (19.00 a pair) and nailed the tabs into the back of the beams in the basement to seperate the laundry area and also along a section of the basement to hide the water heater and furnace and keep that side for storage, took baby pins and pinned the curtains together so they didnt look seperated, spliced the cable and stuck a tv down there put the kids toys, playset kitchen, 2 comfy arm chairs and a small undercabinet frig, painted the wood stairs brown and stapled a runner down the middle. If you just have studs for walls can you just buy those big sheets of primed beadboard at HD and nail it up? I might just take burlap material and nail it to the beams to hide the pipes and wired all over the bare ceiling. The kids love it...not so scary anymore. Good luck!

There is no hard rule in residential use as to the number of devices on a given circuit. However, generally, you don't want to have more than 80% of the circuit rating used. That's easy to compute with lights, but receptacles are a bit more loose. Yes, you can make junctions in switch boxes. You have to compute if it is big enough. Here's a neat little article that explains box fill rules: http://ecmweb.com/code-basics/box-fill-calculations Note that the bathroom has special requirements. It must have receptacles fed by a 20A circuit that either serves things only in that bathroom or only receptacles in this bathroom and other bathrooms. The receptacles there must be GFCI protected. Note that while this isn't an electrical code issue, many building codes require a ventilation fan (especially if there is no operable window). The whirlpool probably needs one or two dedicated circuits. You'll have to read the installation requirements for the tub. They probably also require GFCI. There's no real NEC restriction on height. Note that each point on the wall needs to be with 6' from a receptacle (horizontally). 12" or waist high are fine for this. You can use ones up on or near the ceiling for this requirement. Note that all (120 v 15/20A) receptacles in UNFINISHED basements require GFCI. In finished basements, you're OK omitting this provided it's not one of the specially mandated areas (near sinks, in bathrooms, in laundry areas). More modern editions of the code require AFCI protection on anything that can be construed as living space (earlier ones only require it for circuits feeding outlets (lighting or receptacles) in bedrooms).

Where I am, HD carries the 4' high rolls. However, since you only need a small amount, just use the smaller rolls or batts. Extruded polystyrene (XPS) and expanded polystyrene (EPS) boards would have to be covered with a fire retardant, typically 1/2" gypsum board.

The basement ceiling height of the house we lived in when our kids were teenagers wasn't much higher than yours. My husband sprayed the underside of the main level floor matte black, covering all pipes and ducts. If you DIY, be sure to use a good respirator mask. Our son was the same height as your husband (now slightly taller) and my husband was just a tad shorter. Neither one was bothered by feeling as if they were about to bump their heads. We had no issues with dust. As for noise in the basement, I think it was only noticeable when someone overhead wore high heels. I didn't find that the sound of video games or movies in the basement carried upstairs any more than in a later house with a drywall ceiling. My family liked the look and I was happy to put the money that would have been spent on a finished ceiling toward other things in the house.