Game Help: Multiplayer on 3DS

Hello people!
So I've got some money to spend and I was thinking of buying a 3DS. Thing is I want it just for the pokemon games which I want to play online with other players.
Now, which Pokemon games released for 3DS are still available to play multiplayer to this day and ho much wiil this be possible(until they close their servers or something)?
Thank you!

Oh and if the console I buy is modded somehow would I be able to safely play the games online ? Of course those being legally purchased.

You can probably still find people playing the Gen 6 games (XY and ORAS) online, although the Gen 7 games are likely to have more people on them.

I don't know anything about console modding though, so I can't help you with that one.