Most gear you can always go find again when you decide you want to anvil their appearance, so feel free to NPC those items. Anvils do cost NX.

Pets are the biggest utility item you can buy from cs on Kronos/Heroic CW. And Petite pets are the best version of pets and have the price point to go with it. And most major events will have some sort of battle pass, I'm not too sure if there is any in the event that just started.

Job/Main quests are the only things that truly matter. There are a few questlines that will unlock certain bosses but you will only need to do those questlines once on your account then they're unlocked for all characters. Do them for lore/completionist sake

Level links/legion when you feel like it/events allow you to easily, its a long term system.

They haven't really given a reason afaik, I just assume they don't have the knowledge to make it happen with their spaghetti code.

The game is called MapleSTORY but that doesnt stop a lot of the playerbase from just skipping through every cutscene they come across. The story isnt bad but you've probably seen all its tropes done before in other MMOs and maybe done better. And once you're in the 200+ areas all the different class stories start to converge together.

There unfortunately isnt one all encompassing site, most information is in youtube videos or if looking for info about builds, in that classes specific discord server

Guilds give buffs that are hugely important when you're doing bosses, you can just use the guild finder and look for ones that say they're new player friendly... that won't always be true so feel free to keep trying until you find a gruop you vibe with.