the sizes are awg 22,20,18,16,14, for most stuff so far. some 8 and 2 as well but not nearly as much.maybe 20 feet would do. i got vans harness but would not again. the smaller stuff i got in addition to the harness at 50 ft lengths, some i may not use and others may require more. really depends on your set up.
if you got vans harness you shouldnt need any #8 or #2. if you want swithces and breakers get the ring and or blade terminals red and blue.
ring terminals should be for # 6 screws. ive got a bunch of # 8 terminals that i'll never use. but you made need 10 or so of each (maybe) i really got beat up here and will have a collection when im done but i use stuff like this all the time...DO NOT USE CHEAP TERMINALS LIKE HARBOR FREIGHT. they pull out buy hand the barrel wall thickness is about 1/2 of the good ones
I bought mine from stein and B&C. i bought some GB from lowes and tested them to 40lbs held fine. ( no i didnt use them.....yet)the lowes brand had heat shrink made to them...they were as much or more than the aircraft guys.
the terminals from steins and B&C look alot more robust however.
most everything you need is at steins
http://www.steinair.com/tools.htm
my favorite tool from him is the red and white pin removal tool. and just as his add says the other cheap brands are not very useful