Need some help, advices From SEO guru's - Please must read!

Hi SEO guru's
I'm interested in learning SEO from a long time, i learn few things On page, Of page SEO and blogging abit. however i don't learn them properly and don't give much time because of projects. so now i decide to learn SEO in proper way, i will be giving it time daily like 1-3 hours so the first thing i want to know from SEO experts is that should i take start from Blogging if yes then from custom domain or subdomain blog?

i already have domain which is  tutsoftechno.blogspot.com . It's domain authority is 90 i don't know it's domain authority get 90 :P . it having daily views and there is only few posts on it.

I want to know:
1. How it's DA is 90
2. There are few posts on it but it's still having views? how? cause of domain age?

in 2016 i join youtube and start videos on programming tutorials so i made my blog for it.
my youtube account get terminate and my all struggles wash away.. i got so frustrated because i have been trying to make my source of income in order to stand on my own feet. Few months ago i start freelancing and from that i earning enough Alhamdulillah . 

i start learning programming when i was 13 years old. Today i'm 18 and i learn everything from internet no one help me except stackoverflow and other websites, my first langauge was PHP :D .
But anyway SEO expertise please guide me, i want to learn SEO so any advice and answers to my questions are welcome.

If possible can i have any way to get in contact with you ? cause i will be need of asking questions and there are alot of questions that i got while learning any kind of SEO topic.

Don't worry i will be not disturbing you. I can understand about geek guys are always busy. i will just put list of questions and then you can help me whenever you are free!

Thanks alot much appreciated!