I've used my fare share of braided sleeving...it looks so damn good. especially compared to typical flexloom or tape. as far as tips..lemme think..
first..the 1/8" stuff is just that...basically its for a single wire no bigger then 18gauge..maybe 16...if your patient enough to string it through. this stuff is like an infinite chinese finger cuff, you gotta slinky it down the wire(s). I'd say get your harness kinda 'roughed in' as far as what goes where and tape the groups together in about 8" incriments, then put the sleeve on. what I like to do is use a good electrical tape on the end to tape about 3/4" of the sleeve onto the wires...then follow up with heat shrink over abut 1" of the sleeve and wire...makes it look like a million bucks. the diameters are pretty spot on, obviously you can put bigger stuff on smaller harness but it can tend to get kinda weird if its too loose. there is also a woven sleeve material that is split down the length and has little strips of velcro along the split, so you can put it onto harness that might be hard to get to or ones that might need to be reopened in the future...I'll have to look to see where to get it...I wish you luck with your project though.
there are a couple varients of the split woven loom here:
http://www.cablemarkers.com/braided.htm