I want to ask a few questions regarding music grading

My current situation is that i can only play the drums properly, self learnt and played for 4 years.. A song ill decently play without a problem for example is smells like teen spirit?

And Whiplash is a song ill have to look at a simple tutorial to learn( just describing my drumming ability for now) And i cant read scores without problems haha..

Im looking to learn the piano,guitar, singing and saxophone.

Of course i wont get there easily but i am uncertain of how busy i might be but i always want to learn music no matter, knowing how schooling for music is like i know it is a hassle to learn grading sometimes.. Thats why i want to know if its really worth the unsatisfying part of learning grades../is there a route where i can take with grades that's comfortable for me? I am getting increasingly busy,and broke for lessons tbh.

1.) Can i self at home, then just take the grading exams? Would it be tons better for my current situation? (Isit possible, and should i do it? At least for my drums.. And i got someone to help me for guitar.. I wont mind for all that i want to learn, i find myself somehow good at self learning anything, even chemistry!!!)

2.) Should i even actually take grades.. Does it help? I dont look to take music university degrees or colleges.isit worth it? Or is self learning the techniques all ill ever need? I do look into going into the professional music route, something like a band, not small gigs,but a full time band

3.)which one then, should i go to?