I’m not sure what the VH means but as vtrials go in general, it totally varies and depends on how much unavoidable damage you will take, 16k is fine for most but 20kish (with group buff) is what you need for some of the hms.

The goal is to be out of one shot range. If you are at 17.5k with ebon then you are out of any of the one shots that are survivable for DPS (for the most part). More health is nice but only so long as it doesn't compromise your ability to do your primary role (dd / heal) so if you are above that and haven't made any compromise then awesome.

Depends on the trial. Something like Sanctum Ophidia is a pain since you take constant damage and lined up ticks are a huge risk with low HP, on vAA, it's only the Varlariel explosion and some combos in HM that can kill you. In vMoL, vHoF and vHRC, you can avoid pretty much all damage and run as low as 15k without trouble if you know the mechanics.

Then, depends on which defensive buffs you get, between Minor toughness, Major ward/resolve, Warden and Ebon, as well as a proper CP distribution. There are many ways to drastically increase survivability.

That said, nothing like blue food and a heavy armor piece. Better have a tiny bit more than needed than one bar below "just enough". You can get pretty high HP on a DD while sacrificing pretty much no damage at all.

if you're running bi food with minor toughness and ebon you should be hitting near 20k, which will make you durable AF. it's what i prefer in all situations.

Depends on the trial, but if you’re not certain what you can get away with, then you should have at least 18k. Survivability is highly underrated IMO, and you can get a large amount of health with minimal DPS change. Shifting resources out of Mag or Stam and increasing health from 15k to 18k is less than 4% DPS loss (and being dead for even a short time will be much more of a loss).