> The number (1, 3, 5, etc) refers to the revision of the specification and in practical terms refers to the number of twists inside the wire (or the quality of connection in a jack).
All of which is very interesting when the frequency is many-MHz or the line gets near a mile long; but pretty irrelevant for in-the-box hookup wire.
It's just small-gauge wire with a twist. For single runs, un-twist and use. The twist is handy for wire-pairs; the 8-color (CAT5 and up) is handy when you have multiple wires going the same place.
Tighter twist has very little benefit in audio, as long as the interfering source is further away than the length of one twist. And if it is closer, tighter twisting won't stop it from finding a way to get in. It would take some very odd situation for CAT6 to be better than CAT3 for audio.
> as it's not shielded, i don't think I'll get many problems with capacitance of the cablling
All cables have capacitance. The pFd of data-cable is in the specs, but figure 25pFd per foot/ 80pFd per meter of twisted-pair. A single wire in free space has slightly lower pFd, but inside a box it won't be a lot less than the twisted-pair. Coax construction raises capacitance to 30pFd/ft or 100pFd per meter, a small increase.
BTW, you can get shielded ethernet cable. It is way-expensive and rarely stocked: data-dudes rely on twisting and good balancing rather than shielding, and turn to the shielded stuff only when necessary.
CAT3- is normally 4-wire, CAT5+ is 8-wire. That may not matter: CAT3 is not used in new networks and voice usually goes on CAT1 or CAT5 these days.
You can get Regular or Plenum. Plenum costs a lot more. If you expect a fire, and you breathing the smoke, use Plenum. Building codes will require it in certain situations where a wire-fire's smoke might get into the ventilation system and fill the building, but is not needed in most networking, certainly not for audio.
As mojo says: solid is fine for permanent work, use stranded if you expect to poke or shake it a lot. The electrical properties, in the audio band, are identical.