When you play a Weaponmaster unit, are you allowed to equip more than 1 gear from other units that already have it equipped?

No. According to RiftJudge FAQ #2992, a single instance of the Weaponmaster keyword only allows you to choose one equipment to attach to the unit.

As specified in Rule 821.1.c.7 and Rule 821.1.d, if a unit has multiple separate instances of the Weaponmaster keyword (for example, if it gained the keyword multiple times), each instance would trigger separately, allowing you to choose one piece of gear per trigger. However, with only one instance of the keyword, you are limited to choosing and equipping exactly one piece of gear.