I bought mine second hand too, love the car so far and plenty of good advice there, I went for 6.5 after considering 5.5 and glad i didn't go that hot, with hindsight 7.5 would have probably been the best all round as I have problems with wheelieing quite a bit. Mine came with a load of spares but so far no problems, I'd get some wishbones though if you're as clumsy as me!
Also, a bit of balast at the front may be useful too and maybe the heavier metal front pivot block.
Cheers
Chris