DirectX

Well, hi guys. I have some questions about programming in UE 4.
1)Since I am learning DirectX recently(its gonna take some time, I am working on the rendering pipeline),and since I found low level DirectX commands a little bit “tricky”, but fun I must admit, I decided to see if I could find a game engine to write in
DirectX.
I used to play with UE 4 some month ago, and since I saw its an amazing engine, I read that it supports DirectX.
So my question is what library does UE 4 use( I read UE 4 doesn’t have UnrealScript anymore,so in what exactly library do developers program?
2)Can I write in solid DirectX?
3)When I try to create a script it says I don’t have DirectX 2013,but I have the 2015 Community Version installed
4)How much does it take to learn coding in UE 4?

     Thanks in advance:)