I’m using my old desktop from 2010. There’s no such thing as a server that can “do it all”, but any computer from the last 10 years would probably be a fine place to start. The more you do, the more likely you’ll be to hit some sort of performance limit, and by that time you’ll know more about what you actually want.
In short, find old cheap/free hardware and start playing around.
My wife regularly has rogue “brain trains” like this. Keeps things fun :)
I did the front-end program on freecodecamp.org a bunch of years ago, it was decent. The challenging part about finding what you’re looking for is that Javascript is used in both the front and back ends (and in a number of other places). Courses in JS will usually focus on backend (node.js is common), but it sounds like you’re looking for a basic front-end course.
Also note that “integrating front end with back end” is complicated and depends largely on the backend itself. In the free code camp course, I did some calls to APIs from the frontend, which I think is what you’re asking.
In any case, check out the Full Stack course on freecodecamp.org (specifically what you’re asking about is covered in the “DOM Manipulation and Events” section).
At some point, someone asked themselves, “what would happen if an entire generation suffered from lead poisoning?” and I blame them for this timeline.
I’m not an expert, but any time I’ve needed to do this, I set up my own router as a client to the parent router, and I set my router (client) as the DMZ in the parent router. Effectively you end up with two routers that are both (more or less) connected directly to the internet, without the two networks messing with each other. It’s also minimally invasive to the parent router (even old stock firmware has always had a DMZ option).
The tricky part then is using the wireless connection as your “WAN port,” rather than a physical one. In which case, as long as you can install OpenWRT on it, you should be fine.
The answer also depends on your level of experience and how much you want to learn doing this. You mentioned you haven’t done this before, but are you otherwise comfortable using computers and figuring things out? Are you familiar with Linux and/or the command line? In addition, are you hoping to tinker around and learn a lot from this, or are you more concerned with just setting it up so you can use it?
There are options for all levels of expertise and technical interest, but I recommend starting with any hardware you already have or can aquire for cheap/free (especially if you’re hoping to tinker and learn more). As another commenter suggested, finding an old desktop or laptop and putting a NAS operating system on it would be a great starting project. Then once you play around with it, you’ll know if/where you want to spend some cash on something better. If you don’t have old PCs laying around, check on whatever you use for local buy & sell listings, you can probably pick up something for pretty cheap.
If you’re mostly looking to play around and you don’t have any extra hardware, you can also try things out in a virtual machine (download VirtualBox), which will let you learn without any monetary investment.