What are hardware and internet requirements to setup an instance?

Asklemmy isn't really a place to ask about lemmy, it's for asking general questions to users of lemmy, jut like you wouldn't ask for Reddit support in /r/askreddit.

Regardless, this question gets asked and talked about in the !selfhosted@lemmy.world community fairly often, here is a (slightly edited) comment I made a while back.

You will need a domain name, you can buy one from a registrar such as hover or namecheap (for the love of all that you consider holy do not use godaddy).

You will need a way to expose the server that you set up via port forwarding or similar on your network.

You will need to set up DNS records on the domain you buy to point to your home IP. You may want to figure out a different way to avoid just handing that information out, cloudflare can help with that. You will want to make sure the DNS records get automatically updated if your IP address changes, which is not uncommon for residential ISPs.

You will need to figure out how to get an SSL certificate, Let’s Encrypt will issue them for free, cloudflare gives you one if you use them as a reverse proxy.

Some of this would likely be easier to do on a cloud provider like digitalocean or linode and could be done reasonably cheaply.

These are all common things for setting up any website, so lemmy docs won't cover them. In addition to those (this answer was just addressing "how to get a URL") you will need to install and configure lemmy, lemmy-ui, postgres, and pictrs somewhere (the join-lemmy docs cover this well).

If you want your instance to send emails you will have to figure out how you want to do that (too many options to cover in this answer).

When 0.18.1 gets released if you want captcha you'll probably have to figure out an mCaptcha provider or set that up yourself.

Not to mention thinking about backups, high availability, etc, etc.

As far as hardware to host on you could get away with like ~$10/mo on most any cloud provider, run it on a Mini-PC in your closet, etc. My instance uses 1-2 GB of RAM, ~13GB of disk (and growing a few hundred MB per day), and ~30% of a CPU (an old i5).

Best of luck.

This depends on how many users you are expecting. For a small instance of tens of users, a raspberry pi with a few gigabytes of storage on a home internet connection would suffice.

If you plan on going big, I suggest you read the status posts here, where the admin of lemmy.world goes into depth on what hardware etc. is used for their huge instance.

This doc link says it uses "150mb of RAM" but realistically I think you'll need a bit more than that: https://join-lemmy.org/docs/administration/administration.html

I'm self-hosting for myself with a 2GB VM and RAM usage is <50% with all the required containers running (postures, etc.)

It all depends on the size of your instance, but surprisingly little. The most expensive part of running an instance at the moment seems to be users interacting/posting. I've had my single user instance running for 22 days, here's what I have found.

Hardware: I was running it on an HP Chromebox G1 i7-4600U just fine, I did move it to a HP DL360 G7 but this is overkill.

Network: I have 100Mbit/s down and 24Mbit/s up, I can't even tell when lemmy is federating on my bandwidth charts. It seems to use very minimal network data. Hosting content or users will increase the data requirements, you'd have to get data from larger instances for a perspective there.

Disk: I'm using 4.7G for the postgres and 6.2G for the pictrs after having the instance online for 22 days. This will all depend on how active the communities you subscribe to are. My pictrs is only thumbnails sent during federation, and I have read these purge after some time but haven't verified these claims.

TLDR; if you have some old hardware around stick a decent sized HDD or SSD in it and you'll be able to host your own instance for personal use. If you have more users or host images on your instance, the requirements will go up so avoid this if network/disk space is scarce.

It'll run basically on a potato, at least with just one user

I've been pretty surprised at how light it runs. I'm running a single-user instance and have a pretty decent amount of subscriptions to various different instances. I have it running on a thinkserver with a xeon at the moment but, even with like 10 other services (mostly chat protocols--zulip, synapse, thelounge, among other random things) running, my load average never breaks 1. If you don't plan on having tons of users, you could probably get away with some pretty impressively modest hardware.