5TB bussiness. I would assume that runs on the same system and shares all the same restrictions as unlimited.
Oh you want to run tests you mean? Sure, I could probably lend you temp access to run some tests. I do not have a significant amount of important data on there right now anyway, so that wouldn't be too disruptive for me. I will look and see if there is a way to grant an access-token without full admin rights that I can retract later. If you know how then please save me the time and tell me how - as I have spent limited time with Onedrive so far. I will wait until you respond for this because it's late now anyway, but depending on your answer I can look at it tomorrow if you remind me.
It's mainly an issue in so far that you can't use hashes between Gdrive and Onedrive. This does remove some options like --track-renames which is very useful for running a backup and not having to re-transfer everything just because some folders got renamed or moved.
I suspect you'd have to use some sort of archiving or merging anyway due to maximum files limit.
Only as much of a problem as you make it I think. 400 char is a good bit less than Gdrive's ample limit, but it should still be more than sufficient given that you just structure the data somewhat reasonably. Avoiding excessive folder-nesting usually does the trick. Really depend on how you tend to structure your data generally, so hopefully you already have good habits 
This topic goes into a fair bit of detail of exactly how much longer crypt makes filenames if you want exact info (need to scroll down a bit and be ready for some simple math )