Q: importing folders from aperture

What kind of folder structure?  Folders with albums or folders with projects?

When you open an Aperture library in Photos, it will replace all projects by albums.  And it will put these albums into a nested set of folders, preserving your own folders.You will find them in the Albums section of the sidebar, in a folder called "iPhoto Projects".

See this document: How Photos handles content and metadata from iPhoto and Aperture - Apple Support

You cannot influence how the Aperture liibrary will be migrated at all.  Everything is automatic.

You may want to have a look at this User Tip:  Notes on Migrating an Aperture Library from Aperture to Photos for Mac