Sorry for the late answer, but I've been busy today.
1. From what I understand you are claiming that they are 4D because you believe that each realm is a different space-time continuum, therefore mergequakes also affect time rather than just a spatial level, as I stated in the previous message. So I'll answer the second point straight away.
2. I don't think it's right to take statements made by Twitter and treat them as a Word of God. Usually statements that don't come from the main canon need to be treated a little differently, certainly not using them as main evidence. However, the first statement does not imply that each realm is a different space-time continuum, even in our own universe there are places where time passes more or less quickly. In the second, however, he talks about Jay's wish, and whether at the end of S6 it influenced Chima or not. He replies that the events of Skybound did not affect other realms, but if the events that occurred have no influence on other realms, then it is logical to think so. Honestly, I didn't see it as a message with the intent of explaining how the various realms are actually divided. Finally I would like to mention that Tommy Andreasen has made some minor contradictions over the years, so I think it is wrong to 100% believe his words without using primary canon to support them.
Furthermore, I believe that they are not different space-time continuums, and one of the main reasons is that there is no need for space-time travel to go from one realm to another. Some examples would be the Fire Temple, which is so close to the Underworld that you can physically travel from one side to the other, the Blind Man's Eye which is a direct gateway to the CK Realm, the Mountain of Madness within the KoM which is a direct portal to Ninjago and so on. Most of the time other methods are also used, such as dimensional gates, I am aware of this, but even the latter are never explained or treated as "space-time gates".
3. This conclusion of yours follows from the other points so there is no need for me to rewrite the same thing as before.
4. Yeah, they are spatial anomalies that in an indefinite time can destroy the world, interesting. If the universe were infinite then this action would take infinite time anyway.
5.My point that the term "infinity" is used hyperbolically to exaggerate the vastness of the universe. Furthermore, even if it is not necessary for scaling, in that message I wrote the things I don't agree with, and that point was one of those, therefore, even if it wasn't necessary, I still wanted to specify it.
6. Oh, my mistake, I didn't notice the clip, thanks for pointing it out.
7. When I say "3D" I obviously don't count time. However, the Ethereal Divide is not anything dimensionally higher; it is merely a place that exists between the realms and contains them, connecting them. It is never explained in depth, as far as we know it exists on the same existential plane as the other realms and is not implied to be superior to them. There may be many possible conclusions in this context, but you decided to say "yes it is 5D because it may be the case".