(1) Expand advanced MATE menu from it's default size? (to accommodate file search results)
(2) Get the file search results in advanced MATE menu itself... just like application search results?
(3) Indexing with file contents, now this one I don't know if it's like this by default of not.
This is not currently possible within the menu itself, and as far as I know it is not being planned for, however if I get around to learning enough Python I am planning on making a menu that will, but it will be its own places menu not within the application menu
Not currently, no. But you should probably file the feature requests
(each separately) directly on https://github.com/ubuntu-mate/mate-menu
so that the developers can take a look.
Off the top of my head, I can tell you that 2 could be implemented
without a huge number of changes, but would still take time to develop.
Number 1 will probably depend on 2. And 3 sounds way out of scope for
the time being, so I'd say not for now.
Ha, yes GitHub is not great at making that distinction... File it as an issue and put something like "FEATURE REQUEST: Blah blah blah", and then fill in the description with as much information as necessary for a developer to understand what they need to do