I have no advice for you about where to start- I've never driven a re;latively stock WRX around town. I would imagine you can use less revs than you think though, once you get the clutch engagement point committed to muscle memory and not trying to think about where it is. I have to driv emy RS like that; the Exedy clutch and flywheel combo I have doesn't like small amounts of slip, and my clutch is fubared (I think clutch judder borked my slave cylinder
) so I basically just "know" where the clutch needs to be when I'm slipping it. Feel is very poor.