Selfhosted

People host stuff on Raspberry Pis, so why not a laptop. One limit you might have is USB speeds, especially if you want to add more drives.

USB to SATA connectors as found in these external hard-drive enclosures are often very bad. You can try to get some better ones and pry the hard-drive out of the case, or if that Laptop still has a DVD drive, you can get an adapter to replace it with a hard-drive that connects directly via SATA.

Can do but be aware that the drive will eventually die, so backup backup backup

256 GB is plenty. I start most of my servers at 30 GB and add space as necessary. Less for Linux.

It will work really well, but the difference between a laptop and a server is operational longevity. Laptops are meant to work for workloads for a few hours, whereas dedicated servers can work 24/7 for years sometimes because of how they are made and tested.

However, if the intensity of workload is light, a laptop can also run for a few months provided temps are well maintained. My tiny RPi ran for a few months till I manually shut it down.

Also, backups and backups.

No reason why it wouldn't work! Worst case the drive is pretty slow, but you do have an internal SSD so you can put OS and databases on the SSD and use the external drive for bulk storage.

I had a RPi set up that way for a couple years, worked fine as a simple NAS and Kodi for the TV!

I'm using a name brand external HDD for mass storage. Still using the internal ssd for everything else but I'm not interested in the cost of a multi-terrabyte SSD to do it internally.

Just have a backup plan in place because drives fail.

Go for it. the specs on the laptop are good enough to run plenty of stuff as a server. As long as the drive can be mounted you should be good. Your backups should be somewhere else.

There are certainly better ways to do it, but lots of people use external disks. I would put anything that needs speed on the SSD (so like a database or whatever) and anything else (media, isos, etc) on the external drive. It's probably also worth thinking about a backup strategy, at least for anything there that matters.

I did this for my first year and a bit for self hosting. It worked great! Really no problems with a USB 3.0 HDD station.

I actually used an HP probook 450 G1 IIRC.

Is the internal drive replaceable? That might be a better option. Alternatively, 256gb is more than enough to install Linux (or proxmox) and serve a lot of useful apps. You only need a ton of space if you are planning on storing media.

That's the setup when I started.

I picked up an x230 with a broken screen and used it as a hypervisor (proxmox 5.4).

I used whatever resources available to me at the time and learned weird networking (passing through nics for a router on a stick configuration).

I used that x230 until the mobo gave up.

Sounds fun. But as others have said, plan a backup strategy like in the cloud or something.