Your engine isn't even broken in yet which means it won't reach it's best idle. However slow it will go now, it will go slower/smoother later. Good chance your idle mixture will be too rich out of the box too as this is the way OS tends to ship them to protect from lean running at idle. This MAY need to be adjusted too. You need to get under the tutelage, in person, of a competent/experienced pilot/instructor and NOT the guy who told you synthetic oil was bad.

No tach needed.