1. You can be detained to establish your identification.
2. Failure to follow lawful orders can lead to an arrest under several methods including the joyously circular "resisting arrest."
3. OC: not that I am aware of for pistols. However not positive on that. I know in country, especially closer to the border its no big deal. ESPECIALLY in country near the border now. Long arms used to be fully legal. As a kid everyone with a truck had a long gun of some sort, and that mostly died out after a rash of thefts. I don't know if thats changed. I do know if you go walking through downtown Houston with a pistol you'll likely be swarmed and/or shot very quickly.