Alrighty! Good question!
The entire series is available on PC via Epic Launcher, and has a growing modding community. However, this is the most expensive approach, as 1.5, 2.5, and the DDD rereleases are not bundled together like the Story so Far pack.
The Story so Far pack is the cheaper option, and is available via PS4 and Xbox One, and bundles all of the rereleases together in one package.
The best way to play them is in order of release, so from where you stopped, you should go about it like this:
Re:Chain of Memories ---> KH2.5 ---> Birth By Sleep ---> Dream Drop Distance ---> 3 ---> Melody of Memory
There are more than that, but that requires getting the DS games, as they never rereleased. If you do want to play them, play Days after KH2, and play Recoded before DDD.
Look up videos of the mobile game on YT.