Most probably everything will be limited by IO. What kind of storage and disk setup is planned? CPU usage will only go up with extensive use of Seahub. Using the clients will require very little CPU.
I think a library can easily exceed 100k files. See also Seafile community restrictions?
The 100k files were a recommendation. It could require some RAM to process many files in a single library. I don’t have numbers though and didn’t run into issues in the past.
Regarding the library size 8 TiB will be possible but I would recommend to use a library per purpose (so do not put everything in a single folder as one might do with other solutions).