If you're completely new to the game you should probably pick up a starter set or two to set you on the right path and get you started
The correct thing to do is put one of every one of them into your contraption deck, but thats up to you
Tamiyo, the Moon Sage doesnt show up in a ton of Cubes these days, but Im happy to give it a home largely for the ability to tap down lands
In these matchups, it's good to loosen your standards in order to avoid the disadvantages that come from starting the game down a card
Personally, I think Kenessos will end up becoming the de-facto commander for the tribe as far as optimal builds go, but I think Arixmethes will be more popular because its just a huge monster
Mana rocks in particular are often also ways to fix your mana (get access to different colors) since they produce colored mana but usually only cost generic mana to play