I ran 1.5-2mm of clearance with PSS9's on another car and did get a small amount of rubber residue on the strut tube but it did not affect handling in any way. I would prefer to have more though and I think 3mm should be the minimum. It also depends on what tire width and tire sidewall profile you run.
Running square will allow more oversteer but this condition can be dialed out by using different spacers front and rear. You could widen the track in the rear with an additional xmm spacer over the front spacer. The offset differences as they vary from stock is important. I will think about the numbers and post later. But a 9.0" front at ET29, and 9.0" rear at ET23 should give the same center line of footpring, but the larger wheel/tire in front will give a bit more track so this would be a bit more towards oversteer assuming 265's at all four corners.