Sandor, your best bet is to ask Penny. Send her a PM. She is listed as 'Penmeyer' in the member list. The system will send her an email with your question (if she has that feature activated?), but she will have to log on to the BFFS site to answer it with her own PM. Alternatively, ask her to post her answer on this thread; that way we can all share the love.
1. Can't really answer that other than the precision used to paint standard colors on a 30mm piece would be little different if using grays. Gray is just another color.
2. I use Liquitex Slo-Dri to increase the drying time on Reaper, Vallejo, and Andre acrylic paints here in the USA. I mostly (by far) use the Reaper paints. Normally, I use plain distilled water; basically no chemicals or minerals, to thin my acrylics. The water is put into an empty Reaper paint bottle and I can release single drops. The Reaper bottles are nearly identical to Vallejo/Andrea. On some occasions, I make a mix of water, Slo-Dri, and Fluidant in a 2:1:1 ratio to thin the paints. This is also dispensed from a Reaper bottle.
3. I believe that PM is using a glazing technique in one variation or another to apply the colors. Liquitex also has a Fluidant (flow-improver) to lessen surface tension when painting thinned colors. The surface tension is what causes the beading. A too glossy primer is also a factor. When using thinned acrylics for glazing or washes, you should unload the brush on piece of paper towel. Just briefly touch the side of the brush to the edge of the paper towel to wick out excess water.
I'm sure there are some European-based art supply companies which have similar products; W&N maybe?
Good luck with your project!
Glen
