Problems with My Magic

[Danthemystic he/him]

I've been having trouble with what I want to do with my magic systems. Their mechanics, sources, and forms of use are things that I struggle with so I wanted to get some help with this. These are the questions that I have trouble with: 

1. How do I combine the Sanderson feel of magic systems with the D&D forms of magic and how they work? 
2. What powers in the universe serve as sources for the magic? 
3. How do I have multiple magic systems co-exist together in a story?
4. Who should get it? A select few, a subspecies, people born with a mark, or everyone? 

I constantly come up with these systems and I don't know how to organize and use them in a story at all. 

[+Invocation]

https://brandonsanderson.com/sandersons-third-law-of-magic/

https://brandonsanderson.com/sandersons-second-law-updates/

https://brandonsanderson.com/sandersons-second-law/

https://brandonsanderson.com/sandersons-first-law/

Take a look through these.