Sorry, I skimmed through your post and missed the part that said you already have one
> I don't imagine KOReader would make it easier to add files?
IMHO it doesn't make sense unless you're going to consume those files with KO in your RM1.
in that case you can use
https://github.com/koreader/koreader...ess-connection.
Keep in mind documents sent that way are not indexed by the program that runs on the Remarkable (xochil).
If you're going to use the device mostly for PDFs then I think you're fine with the standard interface. Also have a look at the very awesome projects that are already available for it:
https://github.com/reHackable/awesome-reMarkable
Most of them are extensions and hacks of the RM software stack, instead of full blown apps that run instead.