Health and healing become more valuable the more damage reduction you have, and damage reduction is more valuable the more health you have. I would say a strategy that tends to work out is investing enough VIT that it reaches your soft-cap, then increasing DEF/RES from there. It's usually not that good of an idea to invest all your defenses into VIT, as intimidating as having 1200 HP may look. That HP isn't too useful if it means you get hit for 300 damage a shot, when you could instead build for 950~ HP and take way less damage than that!

If you feel that your build is lacking in a defensive area, you might be able to cover that with specific equipment, racial or class ability. For example, let's say my two-hand basic attacker tank is severely lacking in magic reduction because I can only afford 50 DEF and 30 RES. You can sort of cushion this with a Nullstone Gauntlet, which grants 10 HP and 10% magic damage reduction, in this scenario. Maybe you can only afford 40 DEF/RES for whatever reason, but you can use Martial Artist's Weathered Body main class innate for 10% damage reduction to try and mitigate that weakness.

However, there are two things I want to emphasize:

1. No build is perfect. There will usually be some kind of weakness, minor or large. Attempts at making this weakness less harsh can be usually done.
    
   
2. Most damage reduction equipment, skills and statuses are MULTIPLICATIVE, NOT ADDITIVE. Meaning that if I have 50% base Phys DR and use Weathered Body, which gives 10% damage reduction? It won't become 60%. It'll become 55%.
   

Additionally, stacking Armor helps you survive even longer as a tank character. It's not mandatory, but it helps.

 

Normally, if your Critical Evade is low as in 30's to 40's, then you're better off using the Giant Gene enchant for your Torso slot. If it's decent, as in 55 and upwards, then it's worth a shot trying out Bleached Fang. Not getting crit'd once or forcing the crit build to stack it to reliably do it tends to be more useful than gaining 10% HP. However, if you don't care about crits, then you can use Giant Gene normally.
 

oh no, my super basic onigan basic attacker stat spread that i made for the sake of a guide example needs more hit/crit rate, but i also want it to keep the evade it has or something close to it

In this example, we are supposedly looking to fit in more Hit/Crit rate. Since you don't ABSOLUTELY need that much Initiative considering how the Turn Order works in group fights, which are the ones that usually matter most mind you....

You can lower CEL and increase LUC in order to not only try to keep an amount of evade similar to the one you had, but also attain more Hit/Crit/CritEvade in the process. Example:

Well will you look at that. I dropped CEL by 6 points and increased LUC by that. I lost 6 initiative, but I kept the 165 Evade and increased my Hit/Crit/CritEvade in the process! This is a good strategy if you don't care much about Initiative or Wind ATK. Personally, I'd say the Wind ATK loss in this case is fairly easy to ignore.

You can do the reverse for Evade builds that don't require much Hit or CritEvade, and instead lower your LUC to increase your CEL. In this case, my recommendation would be to leave your LUC at soft-cap and then increase your CEL to your heart's content (while keeping diminishing returns in mind.)

Now, let's say that you want to optimize this example build's HP. You want to know just how much HP you need for what you want to do, and how much is "too much HP." A decent guideline I personally use is to imagine the average damage you will be taking on that character, and then multiply that until it exceeds the HP you've invested.

So let's say that this 752 HP Onigan takes 150 damage on average. We multiply that 150 until it exceeds 752. If you multiply 150 x 6, you get 900. That means that we would need to have more than 900 HP to survive one more hit. In this case it would require way too much point investment than we'd like to since we're still trying to build basic attacks, so it would just be better to leave our HP where it is even if it looks small.
 

• If you want to experiment with different class combos, feel free to. The game enables you to quickly change between classes and equipment. Sometimes, experimenting like this helps you find what you like and learn the game more while at it.
   
  
• Also, if you feel frustrated when trying to figure out a build, it's usually a good idea to take a break from it then come back to it later. That's personally what I do if I start getting frustrated. It's completely normal to be irritated at this sort of stuff sometimes, don't worry. I do too.
   
  
• You can generally roleplay class abilities as other things so long as they make sense in the lore. For example, you don't have to ICly use the Demon Hunter stances or exclaim them despite running that class. There are some things that can't be roleplayed as other things, I.E Mercana healing in general or the Void, but that's a small amount of cases as far as I know.
   
  
• Having several items that your build can use for the sake of variety isn't a bad thing if you want to do it!
   
  
• Focus on progress, not perfection.