The app version is a good way to learn it too, it has a tutorial and various solo and multi-player modes.

Yes. Cats and birds are the main factions (the ones that focus on board control) others are opportunistic (takes situational benefits). 4 players is the best (2 area control faction + 2 others). 3 is cool too but could looks the same because you need the 2 area control factions at minimum.

If your group is 3 only. I recommend, if you had budget, to get one expansion that have another area control faction, for more variety.

Playing 3 with one single area control faction is less fun, IMHO.