On the F12 key: agreed, that isn't intuitive. SSED uses the space bar; works pretty nicely in the workflow.
I haven't got a clue how projectiles/particles are currently drawn in SS, but my vision for the weapon editor is to have a Preview Mode showing it on a firing loop. Getting the Forge to replicate exactly how SS looks might be tricky, and there likely won't be support for flashy weapons, but the basic projectiles or beams shouldn't be a problem.
Essentially, projectiles are drawn twice; once with the coreColor being applied to the graphic, once with the fringeColor, at a larger size. Both sprites are additively rendered.
Missiles are simpler and yet more complicated. They have a simple graphic component that just uses coreColor and is non-additive. But they can also have an Engine when active.
As for weapons, they're very straightforward. Barrels always move straight back, even if the shots come out at angles; if ALTERNATING, they alternate in the order the Offsets are declared (SS does some process to split multiple barrels in one sprite into quads, using the offsets to cut the sprite up). The only weapons that don't obey that general rule are the animated weapons, which animate a frame per time-interval when active, essentially. Modders can do even more complex things with code, but that's rather outside the scope of this project, heh.
But yeah, I'd love to see this become polished for the major use cases that are the core of building a Faction Mod: ships and CSV entries, weapons, .PROJ files, Variant and Faction files. If the code was cleaned up and the directory problem gets solved, it might be a replacement for SSED (SSED, btw, uses a text file to store where the SS directory is, etc.- and was also made with GameMaker).
The problem here is that when you get past ships, variants, weapons and projectiles, it's almost another project entirely, as SSED's developers have discovered.
It'd be so much better if these things were each executed in different UIs; editing a ship's core variables in a spreadsheet is fairly efficient but only if you like spreadsheets and are savvy enough to spot spellling errorz that will cause a crash, such as selecting the wrong ID for a System, for example. The issue here is that Alex has made this a somewhat-moving target, instead of using proper inheritance or safe values so that mods missing the new variables won't crash.
Building a Faction file should be pretty straightforward- text entries guided by the UI, largely; a few methods in the UI guiding modders to create / link to the proper dependencies (for example, the "speeches" Factions give when you talk to them, the graphics files that show up in different UI contexts, etc.).