I'm not sure how I feel about him doing a ton of fighting. I could have sworn that I remember hearing a bit of OWK's backstory in ANH as it pertains to him lighting his saber in the cantina. I feel like I remember hearing that it had been so long that he wasn't 100% that his saber would fire up. If true, add that to him still having all of the same nicks and patches on his robes from ROTS. I'd like to keep a lot of the old hermit lore if possible.
I doubt that. He never stopped being a Jedi. I'm sure he was checking at least weekly to make sure his lightsaber was in working order. He wouldn't have made a very good guardian if Vader came for Luke and he got there and his lightsaber wouldn't ignite.
If they go the route of the Obi-Wan novel, where he is helping whenever he's needed and doing it covertly (disguising lightsaber wounds, Force use, etc.) I think it would be very cool. I like the idea that when he uses his lightsaber in the cantina, he's making a statement that he's back and not hiding anymore. I think that's kind of why after he slashes the arm off, he kind of flexes and stands there like "Anyone else?". The fact that he stayed in the desert for 18 year or whatever shows the sacrifice he's making and tells you a lot about his character. Not to mention, he was never alone because he could talk to Qui Gon and Yoda.