The Guaco is extra.

Deathblows reset the resurrection timer so yes, you can die at phase 1 then when doing a deathblow on the boss to transition to phase 2 you can revive again.

You can't use 2 resurrections in a row, you have to kill some enemies to unlock the second because it will get crossed out.

Whenever you die and resurrect it puts a black bar over your resurrections, until you kill enemies or in the case of a boss, knock off a health bar. If you use bite down or the hidden tooth to kill yourself you can resurrect without getting a black bar, allowing you to resurrect again without killing anyone. Hope this helps!

No. Dragonrot will not activate unless you experience a TRUE death. If its a miniboss and youre being overpowered, resurrect and run away. At least that way you can save your experience/sen. Always res when you can. There is a slight benefit to waiting just a moment for enemies to turn their back before resurrecting, since you can get in a cheap attack or get some distance to heal.

To put it plainly, the point of the game is to stay alive (by your own power) as LONG as possible. The price of dying a TRUE death (respawning at the Buddha statue) is paid for by the NPCs you meet. Normally, you pay for self resurrection from the life essence of the enemies you kill. So yes, it's wiser to die, resurrect, and run back to a Buddha statue. Narratively, it's your mistakes being paid for by other people. Mechanically, all it does is stop quests from being progressed.

Even if you think the enemy will kill you right away and reviving is pointless you should at least give it a try using the home idol or some other way to retreat. There's really no benefit from giving up early.

not using a resurrection node the first one refills on rest, but the other ones require you to kill and get deathblows to refill it, so it might be better to just die so you can retry the boss without needing to go refill it, especially if you died without doing much to a boss besides, dragonrot is hardly punishing, it doesn't kill NPCs or permanently fail their quests, only pauses it until you cure it, and Dragon's Blood Droplets are plentiful to the point where you're unlikely to run out even if you use them every time anyone gets dragonrot

The only benefit it could ever really have is saving yourself some time against a boss you are having a lot of difficulty with. If dragonrot is already inflicted, and you're not concerned with maintaining your sen or XP, then skipping resurrection when you really screw up in the first phase of a boss fight might be something you're interested in since you know you're going to need that resurrection for the second or third phase.

To summarise what another anon said, there's a reason not to resurrect *twice per life*, in that you then have to recharge the extra resurrection use by killing things. That's only really relevant if you're fighting the same boss a whole lot and not doing anything else. For me it didn't come up til literally the final boss.

try tongue but hole

Well...you can die 3 times every boss battle. In DS or Bloodborne 0 times...so yes, there should be a price for a powerful tool like this. In that case it's your time spent grinding.