Hi Tom,
I have not built the Velarde, but I would imagine it's much like any other kit, and the procedure/process is much the same...
I think the Velarde kit has laser cut plastic, all of the edges need cleaning/sanding to remove the laser cut gloss (burnt) before glueing..
As for drilling holes in fiberglass.. I personally drill a hole that is at least 2 times smaller than the hole required, then open it out with a very fine files..
Because the fiberglass is prone to chip when drilling or using corse files..
I would only use a sanding/cutting disc, or grinder if the hole when finished would be twice the size of the grinder/sanding disc..
Having said that, if for example the freeing ports were 1cm x 2cm I would used a small drill and drill lots of little holes around the marked area, staying well within the marked area, then with a fine file open the hole to the required size..
This is the way I would do it.. others might have other ways..