I wouldn't follow the advice of using Immich. While its a great tool, growing fast and super polished, its currently aimed at photo backup from your android phone/tablet and is not a good pick for a family photo gallery.
To that end I would look into pigallery2 or the very good homegallery, which is still in early stages as well but also quite polished and already working great. They will not replace Immich, but will complete the workflow nicely.
In general the flow is to buy or recycle a pc of anykind, install linux (optional, but recomendes), buy a domain you like from some registrar, setup some kind of remote access from outside to your home, and install the services you want.
The workflow mandatory includes hours spent trying and failing, and also having tons of fun in the process. Don't forget the WAF (Wife Appreciation Factor) which will determine how much fun you can have.
Last, i al documenting all my steps and proceedings while I run down my own selfhost rabbit hole in the above linked wiki (self hosted, ofc).