I have a simple take on that question. Speakers that sound good with music will also sound good with HT. It makes no sense to me to have two sets of speakers, one of which sounds poor with music. In my experience, a speaker with a flat frequency response across the critical mid range will do both music and dialog well. In fact, I'll go so far as to say that the few 'HT specialist' speakers I've heard sounded lousy – but they were extremely loud, especially in the bass range. And that seemed to be far more important to the owners of those speakers than anything else.
¾" wood can always help lessen vibrations better than ½". So can cross bracing in larger cabinets. Usually cross bracing is skipped in smaller cabinets. After you build your ¾" mahogany cabinets, you can always add an internal cross brace or two if you think it's needed. But you can't easily make ½" thick sheet goods into ¾" thick.
The filling in speakers with sealed cabinets helps deepen the bass response. It makes the air volume act like it's larger (as much as 20% larger) than if there was no filling. It has little to do with damping vibrations in the cabinet walls. The type of filling material (polyester, glass wool, real wool, recycled denim fiber, etc.) can also matter, but much less so.
Do you have a drill press? If so, you can probably use hurricane nuts without problem. I don't have a drill press, and when I tried hurricane and T nuts, I had problems. The holes for the nut shafts all have to be parallel. Otherwise the last bolt you put in won't thread properly. I've had much better success with threaded inserts. I use MDF for speaker cabinets and I use the flanged inserts made for softwood or MDF (see below), but there are also inserts made for hardwood.
