Rick,

For structured wire forget the boxes, just use mud plates, terminate
at the box by just clamping the bundle to a near stud so it doesnt
fall back into the wall, boxes just confine things needlessly, its not
high-voltage.

Full boxes do offer a couple of advantages.

1. If I decide at some point I need an extra electrical outlet, I can
easily run electrical wires and install outlets (assuming there's no low
voltage cables in the box).

2. On exterior walls, a full box can be sealed for air drafts and
insulated around. On any wall with insulation, it's nice to have a clean
box to work in rather than hunting for wires in the insulation.

I prefer double-gang boxes for low voltage lines as they give a little
extra room for the cable to bend, as well as giving more space on the
faceplates (I like keystone jacks that let me customize to phone, cable,
ethernet, speaker wires, or whatever). The double-gang box also allows a
second conduit connection. I bring cables up the left conduit with easy
bend to the faceplate on the right, and up the right conduit for an easy
bend to the faceplace on the left.

I do have a single-gang box in our bedroom, and it's a lot more difficult
to organize all the wires in that small box.

Pulling cat and RG6 through conduit is a major pain in the ass
as it sticks easily and wont make turns at all, you'll find out.

In my case, my conduit runs are short 16" stubs to our crawlspace. I
have no problems feeding RG6, Cat5, and phone cables through those
straight 3/4" conduits. But, if I were installing a fully enclosed
system with bends and whatnot, I would definitely use larger conduit, and
probably try to stick with straight runs between junction (pull) boxes.

Best way is to find passages through walls then install access
holes (covered later by heating vent covers) and use the whole wall
pocket or joist pocket to get the wire where it needs to go.

Obviously, a retrofit situation is a lot different than new construction
(or remodeling when the walls are open). The advantage of installing
conduit is NOT having to open the walls later. If you're going to cut
holes anyway, there's no reason to run the conduit.

Anthony