1. However the way I tried to set it up, 3 companions is really more for variety of type and species. The idea was to get to play around with a lot of different companions and magic, to enjoy creating and exploring, since normally in game you get so few chances to do that. Having 3 companions would allow you more choices to pick from when facing an opponent, however with most companions having an HP of 20 it is still possible to win with just 2 companions, but probably not with 1 (though it is possible!), as in most fights characters can lose between 30-40 HP, but consider our rounds will be only 3 posts not 4.
2. They don't have to be very complex personalities, just something to base it off. for instance in pokemon when you catch a new one it tells you their nature, such as brave, cautious, fearful etc. That's more what I'm looking for. Of course you can get complex if you want, again giving you freedom to get creative and explore. This, for instance, would be a great time to test run companion ideas you've been wanting for your character, especially if you can't decide between a few!
3. The type advantages will only come into play in the later rounds as a difficulty setting, and will be very simplified, following something like this:
Time>Light>Dark>Earth>Spark>Water>Fire>Wind>Time
Ice counts as water, otherwise I think all the other companion elemental types are straightforward.
Advantage: A fire type dragon uses fire breath against a wind type kitsune so the Kitsune has to play it off as more of a critical hit (SUPER EFFECTIVE).
Disadvantage: A fire type dragon uses fire breathe against a water type kitsune so it will have almost no effect (NOT VERY EFFECTIVE).