I recommend to use Mirka Autonet or similar product for drysandning.
I have a Mirka Deros 650 orbital sander connected to a industrial vacuumcleaner. 99,9% of all the dust are collected and non the **** are stuck in my nose.

I remove the original celcote with P80 (not 80-grit), then P120, P180, P240 and P400 prior to the primer. Sandning the primer with P180, P240 and P400 prior the topcote.
If you go directly from P80 to primer is there are big risk that the grinding scratches will shine through the primer and the topcote after a season of two.