I'm not positive but I believe that the max number of custom units in WC3 is 100. But blah, I'd like to pass this limit. Any ways of doing it?
Note: I don't mind whether or not the process is difficult as I'd like to try new things anyway. Keeping myself backed up in a corner won't help me become a decent map editor.
What he means is there are certain SLK and txt files you must extract and edit the units within them, kind of like how you would edit a spell. Using this method you can create infinite units.
Don't ask me which files though, because I honestly don't know.
You can either use a hex editor on the .w3u file in the map to manually edit the units, and add essentially as much as you want, or use the unit editor program someone made awhile ago.