So, I kind of interpret "Tiers" as like phases in WoW Classic for example. First tier would be MC/Ony, 2nd tier would be BWL, etc.

yea, one of my buddies plays in korea. He said 1st and 2nd tier is pretty easy to gear, 3rd tier is hard and where you need alts

I think the good idea would be to go ahead and level up alts to prepare for future tiers.

Alts are what keep you out of the cash shop.
Nothing is gated behind the cash shop, if you have alts you can avoid it.

I will roll alts just to lock some of my favourite char names at start ;-)

Never played LA and EU/Na release will be my first time I have a few questions so if someone with LA knowledge can answer them I would be grateful. I watched many guides on YT about how to farm gold and which classes to pick and so on but I couldn't find any video that explains mechanics like stagger, counter, break parts and so on . In all videos streamers mention them but I have no idea how they work and how important are they . My last question would be regarding Main character in PvE and PvP , I decided to start with and main Paladin so I can do all end game content and never worry about not getting into groups for PvE but Since I am mostly PvP player and I always focus that in all MMOs I play I was wondering how does PvP work is LA , can I make death blade for PvP and she can perform perfectly even tho I invested pretty much all into my main or do I need to make death blade my main and invest all into him to be good for PvP . Is PvP gear oriented or gear doesn't matter at all so I could just make Alt my PvP character and be at the top without investing all into him ?

stagger, counter, break parts

Some characters and abilities have stagger attacks, a good example of a high stagger character would be a scrapper.
Bosses have a stagger bar, that will stun them when depleted opening a huge burst window, some raid bosses have stagger checks.
Front attacks.counters usually produce high stagger damage.

PvP in lost ark is purely based on skill, gear is equalized.
PvP unlocks ate an early level, all you would have to do is level the character to enable PvP I think 25 or something.

every class has skills that do the stagger, counter, breaks....but some builds dont even run those skill. Instead of using those skills you can use bombs from your inventory that do the same mechanic as those skills

and for pvp lolkggz is right, everything is equalized, i think you can start pvp at like lvl 27....you get a whole new tab for pvp to distribute your skill points and skills thats you want to use and can change it whenever. The only time you have to worry about gear is when you do guild vs guilds, you use your pve gear on those.

also you dont have to make a blade specifically if you want to pvp, paladins in pvp are pretty much S tier. At higher raitings if one team has a paladin and the other team doesnt have a support, the team with the paladin usually wins.

but yes you can level a character to lvl 27 and only do pvp on it if you like. No gear required

Main is going to be gunlance and paladin, Alts not sure yet, probably make a couple more gunlance and paladin to help their engraving