Weren't the Afghan Arabs nothing more than a dozen guys?
numbered are 20,000 to 35,000
The truth is some where in between those figures.
25,000 (+) included any Arab who drifted into Pakistan / Afghanistan during the conflict. A substantial number of 'jihad tourists' never left base camps in Pakistan. Some never even left their Pakistani hotels. They then returned home as a "jihad veterans" with improved prospects for marriage, employment, and bragging rights at the local pool hall. Others who remained in Pakistan went solely as laborers, skilled construction workers, medical staff. teachers etc. (wealthy Arab sponsors preferred hiring Arabs in support roles).
Ben Ladin spent nearly all of his time in base camps, but led three forays into Afghanistan. Each foray consisted of between about 75-200 Arab fighters. Two forays fizzled out with Afghan groups actually sending the Ben Ladin's group packing on one occasion because they were so incompetent they endangered other fighters. The third and final foray ended in a fighting withdrawl that Al Queda propagandists spun into a victory. In Al Queda lore, Ben Ladin's AK carbine was taken as a trophy during the retreat.
All that aside, Ben Ladin was not the only Arab leading jihad forays into Afghanistan. For example, a rival Arab jihadi leader was killed by a mysterious and remarkably well placed car bomb after refusing to acknowledge Ben Ladin as the Supreme Jihader. Lets say that in addition to Ben Ladin, four other Arab Jihadis led relatively large forays into Afghanistan. That would yield say, 1,200 or so actual Arab combatants.