Hindi naman ganon kalala. Yung stain parang madumi lang hindi pantay dun sa light blue na color parang discolor lang. Kung titingnan mo mabuti mapapansin mo kung malayo hindi naman kita.
Lahat naman pwede i-DIY basta't you know what you're up against... I'm hesitant to give you suggestions on the paint problem unless we have a clear view of what's really wrong... If the stain sa 1st problem mo is really a stain, then in most cases a good paint cleaner or cleaner wax can solve the problem... If it's underneath the clearcoat or the pigmentation itself has been altered, then not much we can do except to repaint that problem panel...
The sanding marks naman it's really hard to tell, most sanding marks are not removable by hand without causing additional marring on the surface.