is it worth it to not pt any pts into enchant and use a demon limb for the enchant? does this work for dualdream users? ie would i get the lvl 23 enchant with synergies with max fire? or what happens here?
It's a good idea to do so. You'll most likely end up with a more powerful Enchant that way.
20 points Warmth (synergy) + 23 Demon Limb Enchant (20 points spent) will be a little more powerful than 1 Warmth + 20 points Enchant (23 points spent).
Level 23 Enchant lasts a long time, 11 minutes. The only problem is keeping it on switch, or running back to your stash to cast it again.
Put a Hel rune in the Demon Limb to make it easier on your strength. Or you could even socket it with a fire facet to give you that little more damage when buffing it (+3-5% fire damage adds to your Fire Mastery%).
Also, those 20 points in Warmth are great if you're using Energy Shield as well.
You'll most likely be spending 20 points in Lightning and Fire Mastery, and if you're using Energy Shield, that's 20 in Telekinesis and a few in Energy Shield as well, so that doesn't leave you with many points to play around with.
If you're only using Enchant only for the +AR% and not the fire damage (which is a bit silly on a sorc) then you can spend the 23 points to get Enchant yourself.
How good of an idea it is depends on your gear. I highly recommend using Demon Limb if you're not playing a super-rich character, but realistically, with a +6 Enchant Leaf Staff, +3 Fire Skills hat and ammy, Torch, Anni, and some decent gear elsewhere (2x SoJ, Arachnid's, etc), you could easily get a slvl 23 Enchant on your own without investing more than a single skill point and without relying on charges from Demon Limb. And the nicer thing about doing it that way is you could then enchant your buddies, you don't have to repair charges, and if you have skillpoints to spare at the end of the build you could take your Enchant past slvl 23.