DF:

My personal preference is the Saito line, but if you are willing to read the instructions (and follow them) you should have no problem with a YS as your first 4s engine.

The 2s/4s business is no problem, or not much of one anyway. Where you might be better served with something less complicated to start is the fuel system. Unless you do exactly as instructed, and make an effort to understand what you're doing, setting the carb and regulator can drive you up the wall. Be prepared to spend a while with the engine on a stand until you get comfortable with it.

Bill.

PS: Strongly advise a tachometer, if you don't have one already. With greater familiarity with 4s it will become less important. wr.