At Index I'd say get some RP's or the new version of the small HBs.
Try to stay with one brand if you can. The exception is when you make a clean break in sizes. (eg I like Metolius for small (1.5 and below) and Wild Country cams for larger.)
For Index I'd double up an the .5" to 2.5" sizes. Probably starting at the 2" and then 3/4" then 1" then 1.5" then 2.5" or .5" Once all my gear was stolen and afterwards I climbed a fair bit at Index without ever buying a 4" cam - I did have one 3.5" and one 3". If I needed more bigger gear my friends had stuff. We never had too many RPs tho. Brass nuts are definately a consumable. In general as you start moving up the grades at Index you'll be relying more and more on smaller gear.
Tri-cams = waste of time esp if you are pushing yourself.