Is it normal for the Finder to be slow when many files are in a folder?
Bulk file & folder moves/copies using the Finder are more easily accomplished at the command line in Terminal. A benefit is that the process executes faster.
The mv and cp commands are what you need. Use wildcard file selection on the source side of the command, and create target paths from dragging the associated Finder icons into the Terminal window. Take a look at the myriad options available at man mv and man cp.