why is it always m for mother and b for father
I suspect M is earlier to sound than B or P, so mother gets associated first perhaps? I bet there's a legit reason!

did you find learning Chinese difficult?

Well, i'm still learning =)

Technically, no. The main challenge is just sheer rote memorisation which itself isn't hard, just time consuming. I still don't get some more subtle things that you might get in English though, like how in English we can say

• The dog walked slowly on the beach
• The dog slowly walked on the beach
• The dog walked on the beach slowly

I can think of at least 4 more. Each mean basically the same thing but there's just something... different, about their intention and connotation. No idea how to express that in Chinese.

Tones aren't really difficult beyond memorization either, although since you can't 'see' them, it's a bit of a pain, and I'm not really sure what to do in terms of emphasis as you would in English:

• The dog walked on the beach
• The dog walked on the beach
• The dog walked on the beach
• The dog walked on the beach
• The dog walked on the beach
• The dog walked on the beach

All valid and subtly different in meaning and intent. I'm not convinced that kind of thing even exists in Chinese, because emphasis would throw a wrench in the tone system (which itself can be discarded as soon as you start singing... and isn't really used in Shanghai, where they mostly just use 2 and 4 - up and down - alternately). I understand there are ways to arrange the grammar to put focus on a particular verb or whatever, but it's not the same thing...

But tbh the main difficult thing is living in Shanghai where everything is in English, working with foreign staff, with an English speaking girlfriend and Chinese people who never want to use Chinese around me because they want to improve English. There's just no opportunity to practice it, so 99% of the time it's just learning for some hypothetical scenario that never happens. The second I stop studying, my ability declines substantially back to a year or so before.

That was a much longer reply than I had planned XD