You're right about Duel, it does reset whenever you cast a spell. It's a bit of a bummer, but... what can we do, we need our spells and regardless the skill is still useful. Maybe that's a good reason to leave it at level 2 rather than 3. I certainly don't have a problem reaching the max it can do, but I'm not there for long before a heal or Might recast is necessary.
About Thelumes - I don't see how there can be a debate about using it or scrolls. It's free, costs a mere 5 mana and with it you don't need any skills or traits at all to go towards perception. Not even on your companion. The radius and success chance far exceeds the scroll's and you don't need to spend a penny.
But... if you decide to save those skill points for something else. Sure, Body Development is a good one. Especially for an ironman. I'd say almost necessary. You can't take any chances.
Oh, and hi Cainus. Thanks for sharing your input
you know, our build's are kind of similar. Mine just has a bit more spellcasting involved.