It should work though it is not on the official list of supported
phones. Since you already have an account you can just pull the sim from
your 6s and put it in the moto and it should work right away.
There are no extra charges. Everything is included already in the price
quoted. Do join a party though. Any large party will do. You share no
details with anyone it is completely anonymous and you end up paying $25
a month all in. It is a no brainer ...