Jim-
I'm in the middle of a COW project myself, and had the same question as yourself.

Easy answer: Make a series of cases with increasing powder charges, one or two cases with each charge. Start the series with a low charge (e.g. 3 grains) and increase a grain in succession. Start firing with the low charge. At some point the case will form adequately. Then it's easy to go back to the lower pressure cases and finish forming them with the adequate charge. The cost of the experimental series will be a few primers, a bit of powder and some COW. Some time will be required to break down the overloads in the series and reload them properly.

It's possible to overload the cases with powder. I used 3-grain intervals, and the cases went from not sufficiently formed to flattened primers in one step.

I've used Red Dot, Bullseye, and 700-X powders. Unique should be fine.

I don't bother placing any sort of barricade between the powder and the COW. The COW gets funneled into the case on top of the powder, and the case is handled gently through packing and sealing.

I lightly pack the COW into the filled case with a rod that fits the neck pretty well. Usually I just squish it down to the base of the neck, and then add a bit more COW almost to the case mouth., and squish the added bit down enough to allow the seal to be flush with the case mouth.

I seal the end of the case with dairy wax. I tried using tissue paper in the case mouth, but it was a bother to get just the right amount. It also fell out when I dropped a case. I found that paraffin and candle waxes don't adhere well to the brass, and it was tedious getting the melted stuff into the case mouth without dribbling it onto the case exterior. Some white glues were not completely blown out by the COW when fired.
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Dairy wax peels off the encased product in a flat sheet. It's pretty sticky and malleable at room temperatures. Just press the wax sheet onto the case mouth like an upside down cookie-cutter, and the case is nicely sealed. The red or black wax looks pretty professional too.
--Bob