Yes flat colours are cheaper to some extent... It depends on the finish you are looking for.
An idea might be having a look at cars around you and finding maybe 2-3 colours that you like and telling...
The B18C7 and ITR 4.7 fd box I run in my EK gets grannied when driving to work and the best I've gotten from 39 litres is 560kms... (Usually about 490 to 520)
I agree with this point, handling and being able to get power to the road is important.
I struggled to get anywhere with my EK - B18C7 as crappy old tyres that had plenty of tread but had gone hard...
Sadly no pics as phone died before getting started...
Spoon strut braces and Apexi World Series N1's in...
New KU31's with lower profile and had speedo recalibrated...
If you want to go through the expense you can change your battery or have your starter motor looked at... IMO from what you've explained , its fine and there's no need.
I don't know if it's related but in my cxi when I changed to a cluster with tacho it wouldn't read properly.
Tacho ran slow (about 1000rpm lag). I put back the original cluster and just use an RSM....