All Wekan data including files is stored to Wekan MongoDB database. You can also store files to harddrive directly instead, you see setting for that with command: wekan.help | less
As can be seen from my Roadmap https://boards.wekan.team/b/D2SzJKZDS4Z48yeQH/wekan-open-source-kanban-board-with-mit-license , currently I'm working on adding Assignee field like Jira, it's mostly already implemented. Also drag handles for more mobile usability is nearly done, some parts still do not have drag handles - other parts of card can be used to drag board up and down with finger, only drag handles move cards and lists.