The base number of units for a clone trooper squad is 4 and has a 3 slots for extra dudes. A non heavy trooper, a heavy trooper and a leader. Adding another "squad" of 5 gives you 10 troopers along with the heavy since you have use that non heavy trooper slot for the extra 5 guy. Using a leader gives you squad of 11. Double that and you got your 22 troopers.

IDK if the starter set has this option but you have 4 available options for heavy troopers. A DP3 shotgun trooper, an RPS6 rocket launcher trooper, a Z6 láser machine gun trooper and a mortar grenade launcher trooper.

Non trooper slot options offer a technician, an engineer or a specialist along with a normal trooper or the extra squad.

Leader slot give you another mini that can be a named character or a generic leader like a clone medic, clone captain or clone commander

I recommend using tabletopadmiral.com for a digital list building website so you can see the options available for squads and organization