I really kind of want an all Alolan Pokemon team, but I have this habit, of making my Trainer's sidekick/main pokemon a Ghost type (shiny if I can help it). I adore ghost types, and I dislike using the starters they give you. I love the starters, but it's just such a common, and lame thing seeing everyone have the same pokemon on their teams because they're major parts of the story. Which is why as soon as I possibly can, I replace my starter with a ghost type that I like. I really like Mimikyu, but it's shiny isn't very interesting. I'm just super picky, and have my own style and way of doing things in Pokemon games. There aren't really any Alolan ghost types that I REALLY like. :s I'm having a tough time making my entire team Alolan.
What about Misdreavus? You can get that in this game, right? That one is cute! Also, it's totally cool that you have your own style of playing! I don't think there is a right/wrong way to play c:
I will only add a pokemon to my team if I plan on permanently keeping it. I hate using pokemon just to pass a particularly challenging leader (hence, why it took me so long to beat Ilima!). That's my own personal quirk when playing the game!