I have 406 coins and a monthly membership costs 399. I know I wouldn't be allowed to spend money on this game (until i become an adult in a few years). Will it be worth it to spend 399 or should i save up?

Depends how long you play for. Yearly is cheaper than monthly, lifetime is cheapest in the long run.

i will likely play for a long time so yeah, ig i should wait

Monthly is a bad deal tbh, if you plan on playing WZ for < 3 years go for yearly, otherwise go for lifetime.

ok

Save for lifetime :)

what is the benefit/perks of a membership?

Check the unlockables or membership page

The advantages are rather small: you can create games with more cards, you can create games with mods, and that's about it.

My account is old though, so I never had to bother much with unlockables.

Nothing game play wise, no p2w, but stuff like no ads (Not even true, wheel and ad boost still need them), Screenshots in forums etc., unlocks a few settings and some stat pages

Mods are huge, also no ads on mobile is nice. Lots of other things too, check out the unlockables page

images on forums is also magical

images on forums is also magical