I don't have a RR yet but ive almost got one but i do have another FW and it runs on a short tech with low to medium grip.
for grip i would go with Jaco nitro shoes 40 shore as any foam tyres around the 40's would be good. If not something softer might work.
springs i would go with a medium stiffnees in the rear and a softer spring set in the front.I also go with 40-50 shock fluid in both the front and rear.this should all make it turn in better with less understeer.
Shock location i would set the rear to the middle space as this gives me a far bit of grip and it does not understeer a whole lot.
gearing i would go with a lower tooth ring i heard the 37t is a good idea as you would make faster laps if you can master the corners at a high speed.
you will also want a bit of tow in at the rear for a bit of extra grip.
areodynamics i suppose this will affect the handling if you get the wrong body so i would go with the Mazda 6 as it handles well for cornering.
once i get my FW-05RR i will be investing in a new engine either a o.s 12 3 port TZ or a techwell as money will come a issue and i have aso swapped the Mazda 6 for the nemisis.
I hope this gives you a bit of an idea
but i think ShAfTy would be the guy to ask at the momment as he already ownes the RR and he runs at the same track as me and hes a little quiker then me at the momment........
he's a bit under a second quicker.
at the momment.
Cant wait for my new kit.