I was wondering if the Master's Guide will include rules for converting 3.x (or older editions) monsters to Radiance? Particularly, if there is a quick and easy way to convert HP to Wound/Vitality...
Much enjoying the game so far!
Glad you're enjoying it!
Monster conversion is the number 1 task, time-wise, so yes, there are some conversion guidelines. There are so many great monsters out there.
In Radiance RPG, a monster's hit points work like this:
Vitality = level * 7 + Con modifier
Wounds is based on monster size (Tiny=2, Small=5, Medium=10, Large=15, and Huge=20). Some monsters like trolls get more, but that's fairly irregular.
Converting 4E monsters is pretty easy. Just adjust hit points, change AC to match Fortitude or Reflex (whichever is better), and remember that some energy types like "radiant" have different names in Radiance RPG. Since 4E uses passive saves and such, there's not much else to do!
Converting 3.5/PF monsters is more work. I suggest this: Start with the creature's CR, not it's hit dice. The CR = the creature's level. Keep its attributes (Str, Con, etc). Then calculate its attack, saves, hit points, and DR based on its level, per the monster creation rules on page 246-247. Finally, map over its other abilities as-is, such as darkvision and special attacks and resistances.