Hello Hosthorde. I have used many other hosts before host horde and there was a tool on their ftp file access that allowed people to edit there configs and txt files on the multicraft i suggest that this should be added here first because every time you need to edit anything u need to download the file edit it than upload it which takes to much time. second this easier and less time consuming. My second suggestion is allowing people to make accounts for free and join owners ftp file access with certain permissions and restrictions. This will help server owners and admins work together with out it being so hard to solve a problem your self.
You can directly edit config files under the "Files -> Config Files" tab in the Multicraft panel. In regards to sub-accounts, the idea has already been suggested (and implemented) at https://www.hosthorde.com/forums/threads/adding-users-to-multicraft.358/