Hello John,
Welcome to the MLO community. Regarding folders:
Firstly, I structure my outline into areas of my life (personal, home, work, community), then roles (&Father / Family, &Earner / Finances, &Home Improver, &Engineer, &SCADA Specialist... - don't worry about the & prefixes - I just use a range of hashtags to help narrow down text searches), then my projects and tasks under each role.
So, in summary, the first three levels of my outline are Area of life -> Role -> Project
To make the most of some of the advanced filter options (TopLevelFolderName, TopLevelParentName, TopLevelProjectName), my areas of life are tasks, roles are folders and projects are... projects. That way I can use those filter terms to narrow down my view to a particular area, role or project.
The other thing I use folders for is for keeping notes, links and information related to a role or project, distinct from its tasks. A folder item can also be thought of a note item, with no start or due date and which won't get completed and checked off.
Hope you manage to up a system which works for you, for maximising ease of use and productivity.
Stéphane