The thing is that the benchmarks for defense are hard to come by, some classes have more defensive help than others. Dragonhunter is one of the class combos that have more innate defense value in their skills. DA from wood lore, but also poison res and vit/bleed res.
For a stable defense the values you need:
About 1000 DA - Maybe down to 850-900 if you are not being hit too much (ranged class), with 1000 DA you mostly avoid getting crit, maybe a few exceptions in Act V - Atlantis. With 850 DA you will get crit from time to time but the crit multiplier is not high.
Elemental and Pierce well past 60, ideally at cap (80), Vitality and Poison past 50, bleed just into the positives. You may need high bleed res in specific situations: Trolls in Act V, Golden Boar, Hell boar from Act 3, also Poison against Chimera or Cerberus. Vit capped for Hades, Fire capped for the last part of Act 5.
If possible, you will greatly appreciate at least 10-15% physical res, but is hard to come by: gear.
About 5k max health if you are not being hit, 6-7k for melee. If you have Nature, health is easy, if you have Defense, lots of health from mastery, otherwise...
There are many skill mechanics that let you avoid this hard benchmarks, as example, rogue poison and bomb avoid most of the damage between fumble and confusion, but that trick is very limited against bosses, so anyways you will want to get as close as possible to those benchmarks at endgame.
Ideally, you put in 350-400 dex and get the rest of the DA from gear and skills, unless dex-focus build. For health, if you don't have good mastery/skill support, is a good idea to spend a few attribute points from time to time. If you plan your build from Lvl 1 and you know your endgame gear beforehand, you maybe can skip investing in health. Mana is a few points if you don't get any from mastery/gear, but is just a quality of life feature (chug fewer energy pots) unless you cannot cast a skill due to not enough max energy.