As no-one else seems to have replied to the parent as I write this, let me just reassure you that if you do ever want to look into using a Linux platform for the server side of your system, it's not so big and scary.
There are lots of Linux distributions. For general purpose server work, something big and well-supported like Debian would be a sensible starting point. You can install a relatively bare bones system to start with, and then use Debian's package manager to install and keep up-to-date most other software you're likely to need without having to build anything manually yourself.
You have several decent web servers available. Apache is the 800lb gorilla, huge but does just about everything and very thoroughly documented. There are some good alternatives like Nginx and Lighttpd as well.
There are also plenty of tools that you can add to do things like load balancing and caching if you need them.
You have several decent database servers available. Postgres is a solid choice for most things if you want a traditional relational database. Again, there are plausible alternatives such as MariaDB if your needs are slightly different. The main "NoSQL" databases also tend to run on Linux if that's what you're looking for.
Almost every major programming language has tools available to run back end code in that language on a Linux system.
Basically, the only thing you give up by moving to Linux on the back end is the Microsoft-specific technologies like IIS, SQL Server, .Net and C#. (There have even been some efforts to get .Net and C# supported usefully on non-Windows platforms, but I have no experience with those so won't comment further here.)
There is obviously a learning curve to configure these things if you haven't used Linux before, so I wouldn't necessarily recommend jumping ship if you're already set up on Windows servers and comfortable administering them. But if you do ever decide to switch, there are plenty of tutorials and HOWTO guides for setting up things like web servers and databases on Linux as well, and it's the kind of thing where you could probably get up to speed on the basics within a week or two of homework and experimentation.