M,M,&H - Barefoot, who it seems is much deeper into the finer points of speaker design, as in, he IS a designer - has taken exception to my claims of hearing noticeable differences using heavier gauge wire for speaker leads. I've always been a "hands on" type of tech (for the last 36 years) and after I heard so much difference between light and heavy speaker leads, tried to figure out an explanation. It made sense to me, but apparently my thinking left out some theory that Barefoot was much more in tune with. As I said, he apparently designs speakers - I only use them, and apparently with less than total understanding. I am hoping to remedy that situation, at least in part, when Barefoot gets enough time to post back as he plans to do. In the mean time, since wire is not the most expensive thing you can buy, if it were me I would still get the heaviest gauge wire you can fit to your terminals. It won't hurt anything, and may help.
As to the parallel running of different wires, this is the reasoning: There is almost no chance of an average studio ending up with a "perfect" grounding system, although some have tried, and come pretty close. So, any and all low level signal wires are susceptible to picking up hum from power wires. Also, in the case of speaker wires, a high power system generates maybe 6 amps of current in the speaker leads at 300 watts. If low level signal cables, such as mic cables, guitar cables, etc, are run so that they are close to and parallel to these speaker leads, it is possible to get feedback because of wire location. Think of these wires as coils in a transformer, whose job it is to take advantage of inductive coupling. Only in the case of speaker leads vs. mic leads, we DON'T want transformers happening accidentally. The way to keep all this from happening, especially in a studio, is to run low level signal wires at right angles (90 degrees) to power and speaker leads wherever such wires need to go to the same places. In an equipment rack, the way I do this is to buy cable trough (Panduit and others make this) and run troughs top to bottom at the rear of each side of the rack. I then run power leads horizontally to one side and down the trough to power strips at the bottom, and I run audio cables horizonatally to the OTHER side, then UP the trough to at least the middle of the rack, depending on how tall the rack is. This is then my common entrance/exit point for audio, whereas all power comes in the bottom. I don't use the bottom few spaces of the rack for anything except fans if necessary - preferably not even that. If the rack has MIDI and/or digital audio cabling, I run it in a third trough mounted parallel to but about 4-5" away from, the audio trough. The current levels encountered in MIDI and digital cables are generally not enough to cause any crosstalk even when run close to audio, but I'd rather not take chances - hence the 4-5" gap. One of the BIGGEST PITA's IMO are wall warts. They can cause hum in an 18" Beldfoil shielded TS cable if it's too close. I've had it happen to me or I wouldn't have believed it. My solution to the wall-wart mess is to get power strips that have 7 outlets each, arranged so that the outlets are 90 degrees different than a standard wall outlet. These will let you use every other outlet for a wall wart, for a total of 4 warts per strip. One of my racks has 4 of these strips mounted in the bottom, 3 of which are full of transformers and the other has regular line cords plugged in. They all are fed from a standard light switch at the front of the rack, which has a custom guard around the switch so it can't be accidentally switched on or off. Sorry, got a little carried away compared to your questions - However, this is all stuff you may find helpful when setting up your own studios...
On the subject of soldering, here are a couple of threads from a board I help moderate - should get you started on the right track -
http://www.recording.org/cgi-local/ubb/ultimatebb.cgi?ubb=get_topic;f=6;t=000182
http://www.recording.org/cgi-local/ubb/ultimatebb.cgi?ubb=get_topic;f=6;t=000192
"by the way...how can i measure gauges?" Shackrock, there are a couple of ways to do this. One, if the wire is insulated, is to read the writing on the insulation. Almost every type of wire you see has this info printed on it. Another would be to get a copy of a book called (no kidding, this is really the name) Ugly's electrical references - and a dial caliper. Then you can measure the diameter of the wire and compare it to the tables of wire sizes. (This book is available at some Home Depot's, in the electrical dept. ) Keep in mind that stranded wire crushes and is nearly impossible to measure the diameter exactly, although you can get close with care.
This post is probably long enough for now, hope somebody got something out of it... Steve