yep, the red/yellow is ign live. Red on a stereo ISO block is normally ign live, and yellow is battery live.
To get behind the fusebox all you need to do is remove a few screws, drop the dash under tray, then take a clip off the side of the fusebox & it'll drop down. Couldn't be easier

As for springs, well I'm glad you figured out the correct answer on your own

Not difficult to do, rears are dead easy and fronts are a little more work. You need a spring compressor to do the fronts, and a special strut tool from GSF helps too, the haynes has the procedure in more detail.