With the newest update to hakchi there are no more game limitson the NES mini, well there still is but that because of the internal storage. So far over 800+ roms have been tested with this update. It also supports folders & pages that it will automatically create and sort games alphabetically.
It’s been working fine with 700+ games and there are no errors. Now it only has 512mb of free space that you can use on the NES mini and would say you could probably get well over 800 roms into it before damaging it. Also always make sure to backup the original kernel before making any changes to it.