Not really in for this, but to answer your questions:
1. Can tool_armor have the NO_UNLOAD flag?
Some parts of the code see it as tool, some as armor. Everything that can be defined for a tool can be defined for tool_armor.
-> Yes, that flag should work.
You will have another problem: tools (and guns) can only be loaded with ammo, meat chunks are not ammo. Ammo is a separate item type (see data/json/items/ammo.json), so meat chunks can not be used to load a tool.
2. Similarly, can tool_armour have the non_interactive_msg, like the lightstrip (active)? I'd probably opt for, "You pet your lapdog."
The use functions are independent of the item type. All item types can have any use function.
-> Yes, but note that the parameter non_interactive_msg is specific to the use_action type. Only the use_action type “auto_transform” currently has this parameter.
3. Does the coverage of a piece of clothing affect its ability to keep a survivor warm while sleeping?
Code indicates that coverage only affect how much damage is absorbed. Warmth from clothing does not use it.