You can add an AFC when ever you want. Even a stock Evo will benefit from at least some high end tuning.
Adding a MBC and setting it to stock boost levels (17-19psi) is fine too, even with stock exhaust. You'll get quicker response and no boost taper.
When installing a MBC you don't completely remove the stock solinoid. You leave it connected electrically, so the ECU thinks it still controlling boost, but you remove all its vaccum lines and cap its nipples.
There are "pills" in the BCS lines, but I ditched them early and did not figure out what exactly they do.
Adding a MBC and setting it to stock boost levels (17-19psi) is fine too, even with stock exhaust. You'll get quicker response and no boost taper.
When installing a MBC you don't completely remove the stock solinoid. You leave it connected electrically, so the ECU thinks it still controlling boost, but you remove all its vaccum lines and cap its nipples.
There are "pills" in the BCS lines, but I ditched them early and did not figure out what exactly they do.