1. In `sys_acl_levels_members` table `IDlevel` is profile membership level id from `sys_acl_levels` table and `IDmember` is profile id from `sys_profiles` table.

2. I think yes, but it's better to also clear `sys_acl_actions_track` table for profiles who's level was changed.

3. Changing level via database will not send email to the user that their level was changed