You can clean it with soap and water, but you'd need to dry and regrease all the bearings (headset and wheels) afterward to ensure that they don't rust. Better yet, just use a wet rag to clean off your deck being careful to not get water in the headset or wheel bearings.
It sounds like your compression isn't tight or you might be missing some parts. Make sure that everything is properly seated and installed, then tighten your compression so that it is snug but still turns freely.
Nope, an SCS won't work as a clamp for HIC because it has a ledge inside the clamp and 2 different different inner diameters for bars and fork. If you need a taller clamp for HIC, look for an oversized triple or quad clamp. However, your clamp should only need to be about 2 inches tall, the same as the slit in your bars.
ABEC is a rating scale for the quality of bearings. In theory, the higher the ABEC rating, the smoother and faster bearings should be. Unfortunately, this isn't always true. You can find cheap ABEC 9 bearings that aren't a good as good quality ABEC 5 or 7 bearings. You can find more information here: https://en.wikipedia.org/wiki/ABEC_scale