a) This is why they created Realms. Easy, click and you get a server. Unfortunatley, it is the nature of servers that if you can't handle using the .jar file, chances are you aren't going to be able to handle port-forwarding and network setup, or anything else to keep the server accessible. It isn't very hard, but it does require a bit of learning.
Alternatively, there is the "Open to Lan" button, which is effectively a "click here to create a server on your computer" button. The same rigamarol is required as the standalone server if you want anyone outside of your LAN to access it, though.
c) Minecraft: Java Edition (Or PC edition, alternatively) still runs on java. A while back they simply started including the necessary java internally instead of needing it to be installed globally. So it is still running on Java, and Java is still there on your machine, it just isn't globally accessible to everything anymore.
d) Minecraft: Windows 10/PE/console/etc is programed in some kind of C, I think. And note that they haven't released server software to anyone other than a couple select partners. There might be a reason for that.