Kit comes with rear 1.5mm anti-roll bar. You won't need to go lower than this, only higher rate. I've been running 1.6mm from the roll bar kit. Just out is the rear hard kit, that comes with 1.8 and 2.0mm. You'll want this, so you can run a lighter spring.
http://www.rccarshop.co.uk/index.php...lizer-set.html
You might not need front bar, but I use the 1.1mm from this kit:
http://www.rccarshop.co.uk/index.php...0mm-1-6mm.html
I run the Alu rear hubs:
http://www.rccarshop.co.uk/index.php...-b-max2-4.html
I think Lee Martin runs the 0.5deg, one way or other to adjust +/-ve toe.
I run alloy shock tops, but kit plastic are lighter and in favour.
http://www.rccarshop.co.uk/index.php...ock-cap-2.html
You'll want the new shock bottom ends, later kits include them however, so yours may.
http://www.rccarshop.co.uk/index.php...-cap-2pcs.html
These stop the shocks from taking in air, the v1 shock bottoms tended to do this. Only had it happen on the rear of my BMAX2, not my 4-III, but I've replaced all.
Front shock tower option is a 4mm, which I've not managed to break, but I think you will be fine with the kit (3mm unless they upgraded it in the kit), if you run a shock tower protector. I've not broken a tower or gearbox top since I've been running one.
Steering crank brace:
http://www.rccarshop.co.uk/index.php...b-max4iii.html
or the new arrowmax alloy part:
http://www.rccarshop.co.uk/index.php...-iii-7075.html
I just picked up this today. looks good.
I run the bmax4-2 rear arms, because Naoto and Lee do. Seem to work ok, but the old ones did also?
http://www.rccarshop.co.uk/index.php...ntion-arm.html
I've stripped out a plastic kit servo horn, after 7-8 months of use. It's 17.5mm centre to centre, longer ones hit the body.
Anything else is either to lighten or bling. In terms of spares, keep a front gearbox. You may well break the top shock mount in a roll on carpet or astro.
Use M2x12mm CS bolts in the bottom steering crank posts, not the 8mm as listed in the manual. mine sheered off after some use, see:
http://www.oople.com/forums/showthread.php?t=153598
Initial kits came with over hardened hinge pins. This should have been resolved now in newer kits. MB models and Yokomo.eu had a free replacement part if the kit was bought from them.
Otherwise it's a good solid car.