I think the enc limit for NPCs is 30 last I checked. You'll just have to manage, or edit the stats of the items you want your NPCs to wear. We can't have unlimited enc on NPCs, as then you'd be able to make them practically invulnerable. On the other hand they'd still have carry weight limits. How much enc limit should an NPC have if not 30? I guess that value should be externalized/jsonized (=made free to edit). 30 is plenty but I think it can exclude certain gear.
Removing the plates from the MBR makes a huge difference, so go with that.
Try a slingbag or a messenger bag. Craft a pair of leg pouches for the NPC. MOLLE is superior, but it's bigger than a backpack. Still, I find slingbag to be plenty for my NPCs.
Were you aware you can manipulate the NPC clothing layers just like your own, and have them remove clothing? You'll have to "walk" into the NPC, and you'll get a menu. Choose 'manage armor' in it. It's possible 'e'xamining the NPC brings up the menu as well.