>>717501471
>How many spinoff games are there in this franchise now?
Zero, which is part of the problem. Every game contributes to the plot in some way. But that wasn't clear when those games were released. For example, people expected Days to just be a spin-off where you play as OrgXIII and learn why Roxas is so pissed off in KH2. But then Xion shows up again in KH3, making Days a lot more crucial to the overall story. Nomura's vision is that every game is important to the plot. Genuine fans of KH2 would have played BBS because that was the game shown in the secret movie of KH2. That game is a prequel and very important to the continuation of the franchise plot.
>How the hell do they release the first two games only to then release the third 15 years later?
The conspiracy theory is that after KH1 and 2's unexpected success, executives at Square intentionally sabotaged the franchise in order to keep the company from being taken over by The Mouse. Hence the lack of new console games for 15 years.
>Are these spinoff games essential?
KH1, KH2, KHBBS, KH3D, and KH3+Remind are the "big 5". But you also need to have watched the KHX cutscene movie before playing KH3. Now, KHUX and Dark Road are likely to be vital to the plot of KH4 while Melody of Memory may not be that important.