There are no limitations, but you've to keep some details in mind:
I did a search on the HD for "Type:MP3" so I could find all music on it since it is scattered between a lot of different folders. My search result returned over 8,900 different files and was roughly 6-8GB (can't remember off the top of my head, it may have been a little more)
Windows uses Indexing Service to speed up searching. The Index only runs slowly in the background to update itself when the computer is idle or at low usage. It may not have had time to finish updating the index list. Be sure to use Advanced Search and enable
Searching non-indexed locations to get all your files in search results
So I did Ctrl+A to select all the files and attempted to copy them to my desktop folder I had created. After a while of watching nothing happen, I attemtped to load something else on the PC, like the control panel, but it was blank, nothing displayed. The "copying files" window never displayed either to show me anything was happening.
Thats because Windows is "preparing to copy files". One of the things it does is to get the filesizes for the entire copy operation to make a better guesstimate about the time the copy will take.
What makes it worse, is that you're using external drive (in USB enclosure?) and they are typically 5400 rpm and therefore slow. Combined with USB speed limit, typical read speed for them is about 30-40 MB/s, while internal 7200 rpm drives are easily achieve 70-100 MB/s long-term average rate.
So, all things considered, you just had to wait more, that's the way it works. Alternatively you could use third-party file manager, or software like TeraCopy to speed up things.
TeraCopy uses dynamically adjusted buffers to reduce seek times.
Asynchronous copy speeds up file transfer between two physical hard
drives. The processes can be paused or resumed.
In case of transfer errors, TeraCopy will try several times; after
that, it skips the faulty file and proceeds with the rest of the
operation. TeraCopy also shows failed file transfers and allows the
user to fix the problem and recopy the problematic files.
TeraCopy can replace Explorer copy and move functions. The author
asserts that it has full Unicode support.
This software integrates into the Windows Operating System and
(optionally) appears whenever you cut/copy files using Windows
Explorer. TeraCopy asks for the destination folder along with a list
of the last 5 destinations used by you to paste the files. You may
choose the destination directly from the list without the hassle of
moving to it in Windows Explorer.