I'll agree with djracer - I intended to put 14-16 gauge speaker wire in my post, but edited it out somehow (Normally if you buy the wire in bulk at the store, it's like t-shirts from Hanes or Fruit of the Loom, it's packaged as 14-16 gauge or 18-20 gauge...), Believe it or not, you can get pretty decent wire from Sears in a spool of 50ft for 10-15 bucks if I remember right. Circuit City and other name brand stores charge out the butt for it.
The suggestion above about not skimping on connectors is also great. USE A GOOD PAIR OF CRIMPERS!! Do not use crappy ones like this:
http://www.installer.com/photos/crimpersb.jpg --- go out and spend a couple bucks on a good pair like this:
http://www.qsradio.com/Regular%20Crimp%20Tool.jpg --- best purchase you'll ever make...Home Depot and other hardware stores sell them. You'll save time on soldering, it's an easy way to do "almsot the best". Not many stereo shops solder these days, but solder and shrink wrap is king!
As for running the power cable along the frame, this is not suggested - I say this because this wire is thick, it is a direct power line from the battery and the longer your wire runs outside the cab, the more chance it has to short out all that power -also - when exposed to the world, you risk corrosion/nicks/oil and heat absorption/other damage to the wire. Most professional fine multi-strand power wire sheathing is not made to handle being outside like that. Generally, inside the engine bay is portected from most elements like water, oil (unless your engine is in seriously bad repair) and heat (run along the upper fender well to avoid heat). If you stick inside there and run through the firewall from the battery, you only have maybe 3' of wire exposed to the elements. If you must run along the frame, keep away from all moving parts and use a wire that is oil/heat/gasoline/water resistant to preven copper corrosion or breakdown/hardening/deterioration of the plastic wire sheath.
The previous comment about Power Antenna leads is typically correct on most modern stereos. Your remote turn-on lead is normally blue in color if there is both a power antenna and a remote turn on lead. I've seen some radios that have only one lead (older ones) and it stays on all the time as long as the radio has power - it works as a power antenna lead or remote turn on.
IF you only have one RCA output? Get a crossover, small equalizer or get a quality splitter from your local stereo shop - run one RCA cable to the amps area and run into the EQ or crossover - but if you do this, you can't fade front-to-back on your stereo
Some quality amplifiers come with a "piggyback" lead that will let you jump the signal to another amp from the first. This is really convenient way to reduce runs. Look at yours before proceeding to see if this is an option (but - again - you can only fade if you use 2 or more RCA cables from diff't RCA jacks!!). Ignore all of this Paragraph if you have multiple RCA outputs on your stereo.
Good RCA cables will come bundled with a remote turn on lead already attached. It's a thin wire. Go to the wiring section at Best Buy or Circuit City - look at theirs - you'll see a pair with this extra wire, I'd almost gaurantee it.
Your wiring to the junction box sounds fine. 14 gauge, through a breaker/fuse within a foot and a half of the battery, back to a distro block. I still suggest using 10 gauge wires for each amp if it's pushing 50w or more - really, I guess it depends on what the amp is wired with inside the guts of it. If you open the bottom cover and the power terminal is wired to the amp circuit board with 14 gauge wire, there's not much point in using something larger - again, you'll only get as much power as your smallest wire will hold. But if you're doing stuff like I do, you need something beefy
Example of my old truck's install:
0 gauge power wire:
http://shifty.org/pics/truck/stereo_...l/IMG_0975.jpg
Amps and capacitor:
http://shifty.org/pics/truck/stereo_...l/IMG_0981.jpg
That's only ~$1000 in amps and wire.
If you find your amps are dimming your headlights, come back and post; I have solutions (capacitors).
One last note: If you're running 10 gauge wire, use a 10 gauge fusible link, not a 14 gauge. Again - a chain is only as strong as its weakest link. In theory, by inserting a 14 gauge link in a 10 gauge wire run, your bottleneck is at the 14 gauge wire.