Yeah- it depends on the individual personality of the betta. Some are mellow some... aren't. I don't think he could "eat" them per-say, but some definitely will stalk and kill other tank mates, if you get a cranky one. They tend to be a little bit on the slow swimming side, and have trouble catching faster fish, but they can also be pretty persistent. Not to mention, the concern wouldn't only be for the safety of the other tank inhabitants, but also for him, as well. He would be stressed, if it turned out to be that kind of situation. Some of them get along fabulously with other tank mates, some don't. You have to be more careful in smaller tanks, as there is less space for them to get out of each other's faces, though. Maybe look for a LFS that keeps some in community tanks, find one you like who is already living with similar fish, and watch him for a bit to make sure he isn't going after anyone? I'd also have the rest of the tank stocked & established, so he doesn't claim territory over the whole tank before adding tank mates, and then have what he sees as intruders added into his space. 75 degrees would be ok for the danios, who like somewhat cooler water, and would be ok for the betta, they're pretty adaptable- but, bettas usually don't do well at temps much lower than that. (they frequently even stop eating at temps under 70, and under 75 would probably be stressful for them.)