EmbedIO VS Metasploit

I haven't used it, but EmbedIO looks like it's another option: https://github.com/unosquare/embedio

You could do something like EmbedIO or self-host an OWIN endpoint. But it's not going to "strip away all the magic" so you can learn C# or .Net or all the other stuff easier. You're just moving the goalpost a bit.

Metasploit

Metasploit: https://github.com/rapid7/metasploit-framework

1-) Learn Hacking on a debian based distro like Kali Linux - I personally started with tools like nikto, camhacker... and then moved to more complex frameworks like metasploit.

I once had to give a presentation about Metasploit, and whether it was ethically correct for the creator to make it free and open-source, available to everyone. And in researching this I realized that there were a lot of parallels between the arguments for or against hacking tools being readily available and the arguments for or against gun control. I'll just list a few quickly:

Metasploit Framework (mentioned earlier)

This phase is where the pen testers practically prove that there exist potential vulnerabilities in the target system. The pen testers do the hacking using an array of technical approaches and social engineering methods to exploit the vulnerabilities. The ethical hackers commonly use Metasploit framework to automatically execute exploitation against the target systems. Moreover, they may install malwares such as rootkit to persistently maintain their foothold and further compromise the target system.