I did think about using fibrelgass filler to achieve a similar effect as mixing beads and glass fibres
Actually until I saw a similar comment on the Euro Nova site I didn't know what the difference was, but you explained it well. I have been using General Purpose Polyester Resin (no idea if it has wax, will talk to the supplier when I go to buy more) and have had no issues so far with separation. I did just google to read about the differences and read in one place that if you are doing several layers the heat generated allows the resin to cure regardless of the wax content. So maybe that's how I have been getting away with it so far
GP Resin does have wax in it. You should be safe. It will cure and not be tacky but may require a light sanding between applications mostly to knock down any raised fibers thus making the next layer difficult to lay flat. GP resin is designed for building parts. Any wax left behind on the surface will get reabsorbed in the next layer of glass and resin. Its what every boat builder uses.
I would not recommend filler as it may kick too fast. I always use some gelcoat and cabosil mixed together to make a thick paste. I brush this into the sharp corners before I start laying my glass. Then I push my glass and resin into the paste when I roll it out. This helps to reduce the chances of air pockets.