Selfhosted

1GB is probably enough to run one basic service without a GUI. If you want anything more than that you're going to probably end up running out of RAM and hitting the SWAP file--grinding everything to a snail's pace. Useful projects here might be to add smarts to something dumb around the house or making an old printer support wireless printing via cups.

Like others have said if you want to tinker, a virtual machine via virtualbox or VMware is free for your use case.

If you strongly prefer hardware, an old PC will probably be cheap or free.

If you really want a pi you'll probably have to look for something that has at minimum 4Gb (which will be easy to outgrow), recommending 8GB+. Note that raspberry pi's run best on the official power plug as a USB-a to micro/c won't provide enough power to be stable and will cause weird issues or crash the pi under heavier loads or when drawing power from the pins.

As others have said, 1 GB RAM isn't enough. It also isn't a good deal. You can get old NUCs for $30-40 with 8 GB.

1gb ram is crap. Hardware capabilities aside it's just not enough to run anything usable for real hosting. Get an old office machine for 50-100 with 8gb or more of memory and it will do infinitely better.

Don't look online, ask friends and family if someone has an old laptop you can get for free. Very likely someone does, especially if you are ok with a bad battery and/or a broken screen.

A RPi3 can work, but it being ARM based will cause various headaches when learning compared to something x86.

Oh, and on the "fail often" thing...
Get a basic/old/free pc/laptop and install Proxmox on it.
Loads of tutorials out there, but the basic installer will get you to a "I'm learning" stage.

Create a VM, install Debian, play around.
Then: create a new VM, install Debian, create a snapshot, play around until it does what you want, restore the snapshot, do the steps that got you from vanilla to what you want. Create snapshots along the way as checkpoints. Snapshot, tinker, restore snapshot, advance.

Proxmox is amazing for learning VMs and server things

Raspberry pis are an easy intro to actually using computers (instead of using something like windows).
Raspbian is great (based on Debian) and there is a HUGE community for it.

So yeh, it's a great started for $25, as long as you have a PSU and SD Card. And an hdmi cable + monitor + keyboard at your disposal (and a mouse if you are installing a desktop environment (IE something like windows, whereas headless is a full screen CLI).
And don't get your hopes up for a windows replacement.

But.... Why not run a Virtual Machine? If you have a windows machine, run VirtualBox, create a VM and install Debian on it?
That's free. You can tinker and play.
And the only thing you are missing from an actual raspberry pi is that it isn't a standalone device (IE your desktop has to be on for it to be running), and it doesn't have GPIO (ie hardware pins. And if this is your goal, there are other ways).

If you really really want a computer that is on all the time running Linux (Debian, a derivative (like raspbian) or some other distro) - aka a server - then there are plenty of other options where the only drawback is lack of GPIO (which, in my experience, is rarely a drawback).
And that is literally any computer you can get your hands on. Because the raspberry pi trades A LOT for its form factor, the ethernet speed is limited, the bus speed is limited (impacting USB and ethernet (and ram?)), the SD card is slower and will fail faster than any HDD/SSD. The benefit is the GPIO, the very low power draw, and the form factor - rarely actually a benefit.

I'd say, play around with some virtual box VMs. See what you want, other than Fear Of Missing Out (things like PiHole? They run on Debian, or even in a docker container). Then see if you actually want a home server, and what you want to run on it.
It's likely you won't want a raspberry pi, but a $150 mini pc that can actually do what you want.

As long as you don't use a DE on it, a pi3 is great for experimenting with server software. I still use my 3b for plenty of things.

So the rasp Pi is very versatile. It won't work as well for certain things but you can also hook things up to it that you wouldn't be able to with a normal computer. It's also tiny. That being said, I'd just spend a few bucks more and get a new one. Raspb pi 3 with 1g of ram is very slow.

Sure, I use them from time to time in my lab to spin up test runs. I also have a cheap VPS ($25/year) that I do the same on. You could also use VMWare Workstation Pro (free) or Oracle Virtual Box (free), on your desktop/laptop, to spin up a Ubuntu or other server, and test to your heart's content. I would think the 1 gb spec on the RPi 3 might limit you somewhat on what you could test run, but I have surprised myself as to what I can jam into an RPi 3. PiMyLifeUP has a ton of tutorials for the RPi. Might want to take a glance to see what's possible, but, for an initial investment of $25 seems like a doable opportunity.

In theory, yes.

Just keep in mind that the CPU is ARM-based and not all container images come with ARM variants.