I run a slightly larger exhaust (1.75 inches) from the cat. Stock is 1.5". Didn't notice anything bad regarding torque down low. In fact it seems to run more efficient. But the change in diameter is so slight it doesn't have much impact. Maybe 2.0" are okay?
I swapped the restrictive stock MAF with a C68 Lancer GTi MAF which I guess is equivalent to a 1G non-turbo DSM MAF. I have an EPROM ECU, changed to MAF calibration tables to the GTi MAF and it ran like stock... In fact it idled much better and runs smoother. It sounded much different, louder, smoother, as even my wife noticed immediately. Judging from the logs I freed up a bit of airflow above 5000 rpm.
I have yet to measure airflow with the larger TB.
With a modified EPROM all issues with these modifications are a thing of the past. As a bonus my heavily modified the AFR and ignition tables yield more power and torque overall, resulting in a much better fuel economy. I consistently get about 5.8 liters/100 km which is apx. 40.5 mpg.
But european CSMs do have knock sensors so I can run on the edge of knock and don't have to worry about destroying the engine.
As for clear indicators you'll have to improvise. You can "bake" the indicators which softens the glue. That way you can open them up and remove the yellow plastic lense.
If you're into more "exotic" stuff you can run euro turn indicators which are completely yellow. They look like this: https://www.ebay.de/itm/DEPO-Blinkleuch ... 4189429373
I do have a spare set of those that I don't need anymore in case you like them.