not thousands. most of them. Tolkien stated that they were ten or something...
Sauron was stronger that the Istari as they were not allowed to show their strength. Gandalf himself stated before the Valar that he feared Sauron. Of course Third Age Sauron was weaker than Second Age Sauron. If the Maiar were to duel with him in full power i think he would fall but to do it they would first have to slay every single orc/uruk/nazgul ect that he commanded... Even in the LAst Alliance when he was much stronger he only came forth after 10 years of siege. I think that the strongest of the MAiar was Eonwe as it is said in Valaquenta that his might in arms was surpassed by none in Arda. Sauron was the greatest of the Servants of Melkor so he must have been stronger than Gothmog