I have both a remarkable 2 and an onyx boox and I am using them for accademic purposes too, my advice is to get an onyx since you can search the documents for keywords (feature I have not been able to find on the rm2),it has a dictionary and far more options for reading (like, the onyx can automatically separate and present as 2 distinct pages those paper written in 2 columns, making the reading far easier Imo)
I have a note 2 (4 years old devices, but still functional) that has a 10 inches screen, and I would not recommend to get something smaller. They have also the maxi series that is about 13 inches, that seems amazing if you don’t have to carry it with you everyday. I would say any model like note 3,note air or newer would be good (not much differences between them Imo, just some small hardware upgrades).
Boox devices run with an heavily modified version of android, so I just create a shared folder between my laptop and the note and downloaded an app to sync them.
There should be also an official desktop app for that, but its servers are based in China, so synchronization was painfully slow for me (from EU).
It is not difficult to move stuff, but rm2 is definitely more user friendly.
Onyx has hundreds of features and it is far more customizable, but the sheer amount of options/menu is, again, not very user friendly. A very cool features of the rm2 is the capability to add blank pages to a pdf, this is something you don’t have on note devices. For the hardware, they seems to have 2 different type of glasses on the display, the writing experience on the rm2 feels better, but that is subjective.
Trying to summerize, is like 10 years ago apple vs android, rm2 has just some features, all very nice and done with a lot of attention to the details, while boox devices does a lot more stuff, but in a more “nerdy” way.