I'm a violin student and woah jikolo I'm having the exact same problem as you have ><"
Cant seem hold the bow right and my shoulder gets tired very fast
Would you mind to share how you adjust your posture so that your would not be tired that fast?
Have you tried using bowmaster? I have one and my fingers felt slightly better but I still cant seem to position them the correct way

Ah I finally found out how to quote
If I just put the violin into position and never grip it, my violin would kinda fall off when I'm shifting positions or doing vibrato
By the way Cello, are you selling violin mutes in your shop? I'm looking for one

How much does one of those cost, I mean approximately?
I'll be using it just for normal practices

From my personal experience, my grades are determined by my teacher
She suka-suka say "okay from next month, you're gonna be grade 4. The monthly fees for grade 4 is.... "
But of course she send me for exams as well for some of the grades she chosen to see if I am par with the current grade standards
I went for ABRSM exams, and will receive an official certificate

I am not really sure myself, but I think its widely recognized.

Almost all of the music centre that I've asked around are using ABRSM exam standards as well.

By the way, ABRSM is not local, its main office is located at London if I'm not mistaken.
Your exams will be graded by examiners coming from London, and theory papers will be sent back to London for gradings, and then they send your cert back to Menteri Pendidikan to be collected