Need help with wheel width and offset

chendaxian888

Hi dear Z family members,
After the suspension and rear diff, I decided to go SPL all family and a new set of wheel and tire just for autox and racing. What I have now:
zeta4 seat
kwv3 suspension
Akebono calipers z1 rotor and EBC yellow stuff
Z1 intake AAM TP M7 Japan exhaust admin tune
Z1 3.9 quafie diff and Z1 solid bushing
57CR 19 inch 9.5,10.5 PS4S 265 40 19, 285 35 19 for daily
I am going to buy:
SPL: Front Upper Arm, Front Outer Tie Rod, Rear Camber Arm, Rear Traction Arm,
Whiteline: Front and Rear sway bar and link set
The Tire I chose for racing is Advan a052,
I want a set of VolksRacing 19 inch 10.5 and 295 35 19 all around, but I think I need do some practice now with lower standard wheels and tires.
So I decided to use 275/40R18 all around with same size spec wheels.
The wheels I chose is Enkei RPF1, I am only using 275 width tire on them so I am considering using 9.5 or 10.5 but I dont know what offset will fit out car best.
Witch off set and width of wheel should I chose? they need to be same