Is it possible to give items to henchmen that they can use other than potions? I am playing a sorcerer and have Tommi Undergallows as my follower,and I would like to make sure what he wields is the best.⁹

No. Some adventures allow more control of the henchmen but the main campaign doesn't even give you inventory control. Just potions (any potion) and some orders through talking and other orders through radial menu.

Henchman Inventory & Battle AI Mod

https://neverwintervault.org/project/nwn1/hakpak/original-hakpak/henchman-inventory-battle-ai-mod