I use anything from 2.5" to 3.5," with 3" being my usual.
Strips are cut cross grain, just like any other strips I would use in my quilt. I fold down one corner into a point on each strip, press, and use the fold as my seam line when joining at a 45 degree angle. Baste first, to make sure the strips are lined up properly; then stitch & trim the seam. I start in the middle of a side, leaving a good 6" hanging loose. Stitch to within 1/4" of a corner, backtack & remove. Miter corner & begin again. When I get to the starting side, I leave plenty of room to manipulate my binding so I can line it up, mark with chalk, and again make that 45 degree seam. It's more important to baste this last bit than the initial diagonal seams. Then I flip to the other side and finish by hand.