I'm choosing a server to use, mainly for HA but I think I'll run Docker on it for other projects. I've narrowed it down to a few options, but am absolutely open to other suggestions.
Lenovo Ideapad Y480. It's from 2012, I already have it and it's gathering dust. Intel i7, 8gb RAM. Battery easily removable, so I don't have to worry about battery fires. It has an HDD that reviewers even back in 2012 were complaining about how slow it was.
The same Lenovo but with an SSD upgrade for speed. Somewhere between $13 and $30 on eBay, I'd have to research what type to buy.
Mini PC (Dell Optiplex, HP Elitedesk, etc). Used from eBay, probably for $80 total, give or take. Would be better suited to being a server than my laptop would.
There's no reason not to use your Lenovo ideapad since it's just collecting dust. It's all depend on what you are trying to run but I can't see it's a problem with your Lenovo. Give it a spin and if it's not up to the task then get a Mini PC after. It's not that expensive anyway.
If you are starting out and not sure if it will be for you then it's always best to try it on something you already have, so use the laptop as already suggested. If you want to run other projects as well consider look at Proxmox, this will allow you to run HAOS in a VM which when starting out will make stuff far easier. Also has very good and easy to use backups.