What kind of DEE Sentinel do you want to play? The acid version is the easiest to work with, but you can also go for the vitality or fire versions.
In my case, I fully intended to maintain the Daega Set for this build, but I also considered using the Rotgheist set because it increases AoE on the skill and adds vitality damage to it without fully converting it to vitality damage. Thus the Leafmane Horn and Mythical Wretched Tome of Nar’Adin can be used to convert the vitality damage to acid.
As a level 82 caster set, Daega has very low armor value, but it also has physical resistance on all three pieces. It can’t be crafted, but sets like this aren’t all that rare. This also works for the retaliation version and you can use the Sentinel of the Three set as well. Check out this build by @lMarcusl if you are interested.
If you want to spam the skill, you will need more cast speed and the Deception of Dreeg set. Or you will need the Ember’s Calling set or the Mythical Tome of Atonement for the fire version. And the vitality version requires the Mythical Hallanx’s Head.
When it comes to just leveling, DEE is easy to work with (if you are using nuke version) and there are quite a lot of options to work with. You can obtain a Groble Toxic Effigy early on and work with that. I suggest going immediately into Act 7 after beating Act 1 and making your way toward the Infernal Wastes. There’s a crypt there with Sister Crimson as a guaranteed spawn. Then you farm her until she drops her Vile Scepter which provides a big offensive boost to DEE while leveling. And before Old Arkovia there’s a hive with another boss you can farm for the Ronaprax’s Sting. All of these can be obtained pretty early on and this gives DEE some serious power. Just remember to periodically farm the MIs again after certain level thresholds (30, 40, 50 and so on). I hope this helps! And feel free to ask if you still have questions.