A couple of tricks I have learned. Air blower works well, but the powder goes everywhere. I use a shop vac and a nylon brush end to vac the sandpaper. Another thing that works well is a cheap piece of carpet. Wipe the sand paper on it and it will be clean.

600 under base is a good place to be.

I'm not in favor of using a white base as a sealer. I understand the white to give the orange a pop. But the white base is NOT A SEALER. A sealer will provide a barrier between all the substrates used before the basecoat or first layers of single stage. It works to keep different materials reacting differently to the solvents in the new materials. A base paint will NOT DO THIS. The result can be different appearance of the base in different areas because of what is under it being different. A sealer will make it all uniform. Many sealers have a window of use, and if sprayed and top coated within that window you will be good to go. Outside the window and a scuff sand or reapplication is needed.