If you need some pointers on how to gear your DH, you can take a look at mine.
To improve the gear you currently have it depens a lot on your budget.
The first thing I would change is the chest, get something with ~240ish vit. Second would be to buy some vile wards, it will be a huge boost in EHP. You can get a very nice pair for 50-80m. Of you can craft some, but it will take a while to get a good one.
Then get some decent gems.
If you find yourself dying a lot, I would change marked for death with companion: boar. That should give you a nice boost in EHP.
A piece of advice: if you're looking to farm paragon levels with the same efficiency as you do with the barb, then the DH is not for you.
After you farmed anough demonic essences, craft some bracers and amulets. If you get lucky you can get a 10-15k dps boost from each, but it will take a while to get a really nice one. My amulet took about 800 crafts -.-
The last piece would be to get a nice manticore, but that will be a 1bill+ item, and I don't know what budget you have.