Unfortunately, mission designers do not always state in the summary (the text you see when scrolling through the list of missions) what vehicles you will be controlling, the terrain over which you'll be fighting, etc.
It's impossible to say what missions you "must" have in your collection. It's too subjective. I prefer missions where you control only a small number of vehicles. It seems like most designers like to "go big."
If you like the M1 series, some smaller missions that come to mind right away are GaryOwens' "Camp Hornfelt" series, Zipuli's "Tank Platoon in the Attack (M1A1, winter)" and <shamelessPlug> my own "Platoon Tactical Movement - Ft Knox 1 - M1A1" </shamelessPlug>
Also, the "Tanks ProPE" scenario is a good one for learning how to operate a single vehicle tactically.
I believe all of these missions are located somewhere on this page:
Steel Beasts website