Hi Nedetheo!
1. To add a weapon you need to create a dummy ability (create a new ability ex: Item Armor Bonus +1) and set defense bonus to 0. At Art - Target add the weapon model you wish to add to the unit.
At Art Target - Attachment Point 1 write "hand,right" or "hand,left" (right or left hand to attach)
Then give the ability to the unit.