First sand everything down with 120 grid sandpaper.
For the larger gaps I would not use spot putty. Use a 2k putty instead. It is much harder and fills the lines better. You can also use a 2k epoxy putty like Miliput for this.
After filling, sand everything again with 120 grid. Then give it a 400 grid wet sanding.
Then apply 2-3 layers spray filler. A... See more