So if i use four regular clawdites ,on the fourth i will use NO Form card? ( i believe there are only 3 in the supply)

While there are 4 Clawdite Shapeshifter plastic figures, there are only 3 deployment cards (and 3 Forms).

i believe this is the recommended number for skirmish and its the maximum that can be used in their campaign

In skirmish they’re adherent to a maximum of 4 regular and 2 elite groups.

Yes, there are three forms and all are Unique . So, if you are using greater than three Clawdites a maximum of three may have a form card at any given time.