Would you suggest me to play the first games in order to get a team for S&M before they come out?
nah
>using pokemon from different gens during you story mode playthrough
Can't do that until January.
>>29316509
I would suggest you play the earlier games before SM because they're fun, and going from a full 3d game to flat sprites and gimped interfaces/features is a little grating so you might be put off if you start with the latest gen and work backwards. At the very least try one of the GBA games on an emulator.
>>29316509
Yeah. Try yellow if you want some color. Those pokemon will have special stuff says ohmori when transferred to sm.
>>29316509
Depends, do you want to play in January on in November?