I just bought my first one from Custom Dioramics. Anyone with experience with these things? I hope they are better than resin (Ew that awful dust! ) Thank you.

Yup
In this thread - To Each His Own



They are nice, nice detail even in plaster. The fit can be fun to figure out, usually no instructions. Most are straight forward, just take your time.
I would look to use the pin/hole method of reenforcing the joints. There hasn't been a lot of sanding for fit so I think you'll be happy.

Beautiful diorama, and colorful instead of drab.

But what's the best undercoating between the plaster and outer paints? I was planning to use Floquil acrylic railroad colors on what I have.

I use hobby acrylics almost exclusivly on buildings. Brands like Apple Barrel - you find them at places like Michaels or Walmart. Cheap ($1/bottle), thick, decent coverage, huge variety of colors. Then I go over that with model paints or oils.
In this one I used a corn/tan base, gray base (mix of black and white), and brick red. Then I used a burnt sienna was on the yellow, a huge mix of reds on the bricks, and a mix of oil blacks/grays on the the stones. Then an overall burnt umber wash with some black pin washes.
Oh yea - the green is a base of pine (?) green hobby paint, then oil washes to tone it down and blend it in.

Thanks for the complement.

Nicely done Scott! -I prefer plaster to resin -but that may just be a preference. I think that it more closely resembles the prototype ( the real building) and I really like that it can be broken or carved easier and more realistic with much less work. In the 70's plaster was the choice for dios mostly hydrocal -its light and strong and takes a finish well.