With 256 patterns and 64 parts to me it seems quite reasonable to fit an entire set or even several sets in one project. I suggest keep filling up one project instead of creating a bunch of smaller ones, organize material by bank or even 1/2 or 1/4 bank.
If you have multiple projects to combine into one it’s possible to copy and move entire banks of 16 patterns / 4 parts using the OT file manager or a computer, if needed copy patterns/parts from multiple banks into one free bank and then copy/move that into master project. I always just add to the same project and only save to new (then immediately save) to keep backup iterations but never start another project just for new material.
I am however live loop based so I don’t run into filling up sample slots and I get a lot of mileage out of a pattern and part, but still an OT project seems like it can go quite far for more standard sample based workflows.
Look up the “transition trick” for a great way to move between material, of course there’s lots of other ways to do things too…