flat dropouts are traditional. Caps are for people that weld and are a relatively recent development if you consider all of bicycle building history. Most people that braze will cut slots in the stays for a flat droput. With 3 frames built, you probably can fill the openings with brazing filler. Probably best to get steel so you can fill with brass if you go that way. I have always thought that flanged dropouts would work better with welding because it's hard to build a decent fillet. People do it, no doubt.

Anvil is still selling dummy axles. Paragon is going to take over that business since Anvil is shutting down. The anvil dummy axles were always sized to work well with Paragon dropouts. I assume Paragon is going to be making identical dummy axles to the Anvil ones.