Apparently you do not have any gas, water or electricity hanging below your joist. Unusual. Then, no problem hanging drywall from the joists. This will give you additional ceiling height. The one "con" which comes to mind is that you have no space for the future to route anything through the basement going across the joists. That means future electrical needs, cable or the like. We had utilities hanging below our joists so it was necessary to "bridge" them and I hung 2 x 4's flat and attached the drywall to them. Benefit is that I have access going both directions. May not be necessary but I like options.

The choice is not a matter of one being better than the other. Where a wall contains a door, the difference in GWB thickness will have no effect on actual sound transmission and the thicker GWB would probably require a custom door jamb size or a trim shim (if the buck is not split/adjustable). Where there is no door, and acoustic separation is important, it is better to use one layer of 1/2" GWB on one side and two layers of 1/2" GWB on the other (imbalanced wall) which also avoids having two kinds of GWB on the job. The next step in acoustic separation is double layers of GWB each side and then adding acoustic dampening systems like resilient channels, Isomax channel clips, acoustic drywall (dampening layer), or green glue (assuming there is not enough room for a double studded wall). How a wall is sealed at the floor and ceiling and how many penetrations occur (especially back to back - insulation is effective here) is often more important in the real world than the wall design. Sounds will easily find and travel through cracks; make it work harder. So, 1/2" GWB is fine if you use it wisely. Mark up the plans in red with a symbol for "double layer" (eg, D.L., heavy line, etc.) on the appropriate side of an acoustically improved wall so the drywall contractor will know what you want. Try to trade the additional GWB for the thicker board. Regarding fire protection, non-fire-resistance-rated GWB disintegrates to quickly (as it gives up its water in a fire) for the thickness to be important. For better fire protection you must use fire-resistance-rated GWB and in that case 1/2" Type C is as effective as 5/8" Type X especially on the most important surface, the ceiling. The next step in residential fire protection would be to use solid core doors and then add a closer (or just forbid smoking in the house).

Hello mmmmmm, His approach and your descripton seems appropriate. >> Primed drywall can seem "rough" to the touch because the water in Latex primers does tend to "Fuzz-up" the outer paper-layer. Therefore, the light sanding he'll be doing is necessary...ESPECIALLY IF you'll be doing a higher-sheen paint like Satin or Semi-gloss. ANY little variation in wall texture is magnified by the higher sheens. >> In an ideal world, even rolled primer should be sanded for the BEST appearance. >> I'm real glad he's rolling the actual color coats!! This puts much more paint on the surface (per coat). It would take about FOUR spray coats to equal 2 "rolled" coats. Hope all goes well! Faron

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.