There's a lot of excellent advice in your post. I agree with your 870 choice. Were I to fish in grizzly habitat, I'd want an 870 & slugs. As I see it, a shoulder-fired weapon is best self-defense.
I never carry a handgun while hunting. I do while fishing back country, black bear habitat. I always avoid bears. If they meander into my fishing areas, I leave. I have no interest in killing a bear. I do have a compelling interest in saving my kids' lives.
I do not own a large caliber handgun. As you pointed out in your post, frequent practice is important for proficiency. I do not enjoy shooting large caliber handguns. Heavy recoil ruins fun. I can fire hundreds of .45 ACP rounds all day every day. It's a fun caliber for me to shoot, especially out of a full-size 1911A1.
There are essential factors that I consider when carrying a handgun; i.e., suitability (will it work), reliability, speed to battery, sight picture retention, ease of operation, reloading speed, and portability. Limited to black bears, lion, and bad guys, no other weapon suits these factors for me as well as a 1911A1. It's an easy weapon for me to conceal carry.
Bear spray and pepper spray in general might work, but there are potentially deadly consequences attached to it. First: conditions have to be completely advantageous before using it. It there is slight potential of incapacitating its user; e.g., becoming blinded by it due to wind, I would not want to use it. Pepper spray is effective on 90% of people on which it's used. I know it will drop me to my knees in agony. I've heard bear pray is worse; however, I have read conflicting reports about its efficacy on bears. On my knees in agony would leave me helpless to any attacker, man or beast. The second disadvantage of pepper spray is its effective distance. One surrenders all options to it. Were it to fail, one would assuredly be unable to bring a shoulder weapon/handgun to battery in time to save one's life.
Surrendering a tactical advantage is never wise.