I got my first full-conversion (if you can call it that) mission done.
The whole thing is a bit buggy, but it's got custom weapons, custom sounds (some, not all) and most importantly, custom ships.
I have a video of me playing through it (because I still wouldn't really consider it safe for release...)
The only real issue so far is that the "sabotage subsys" for all engines doesn't want to go off at the very end.
Also, my most recent (and so far, the best one I've done) creation:
Modeled after the 194X Fubuki-class Destroyer (minus the torpedo launchers).