You can try each one separately to see what they are. You do not have to choose only one.
Just a few that stand out among others: Essentials does not have fancy brush options, it does not have a node system, the effects are very limited, it only has a bone deformer no curve, game or envelope deformers, it does not have the underlay layer or the overlay layer. It only has the line art layer and color art layer.
The most expensive option aside from buying a permanent license is to pay month by month. You save paying for a full year all at one time. But if you only want to try it for a few months that is worth paying a higher rate for because you can discontinue it after the short period you use it. And then later if you need it for another couple of months you can subscribe for those couple of months then discontinue when finished. So if you don’t need it everyday you can access it when you do need it. You would be saving a lot of money by not paying for all the time it sits not being used. And, there is no point in owning it in the form of a permanent license when you don’t need it very often and for very long periods.
“A pain” is relative. My feelings about the “Return License” process is that it is an easy process it is just impractical sometimes.
About 2, Essentials only has one layer, no sublayers at all. It doesn’t have bitmap brushes or textured vector brushes, and the Pencil tool has no pressure sensitivity, so unlike other versions the Pencil is not very good for cleaning lines, except if you want a flat, uniform thickness line (you would use the Brush tool for that purpose). It only has bone deformers, but includes the game mode option. You’re also limited to export a 2K/HD file. It has only seven basic effects (like blur, glow, etc.), Advanced has 12, Premium, I’m not sure (there are 40 on the filter category, there’s much more nodes, but not all you would consider an ‘effect’, since some are used to built effects).
