Well if you want a proper upgrade, 40TB plus redundancy and space for a GPU, I’d say you don’t want a mimi PC but a full-blown one. I built my server myself from components. It’s hard to find good numbers on power consumption and that was one of my main concerns. I had a look at some PC magazines and what kind of mainboards they recommend for a home server. Figured I wanted 6 SATA ports and I started from that. Unfortunately said magazine doesn’t have a good article right now, so I don’t know what to recommend. Another way is to look for refurbished PCs. If they’re some brand like Lenovo or Dell, you’ll find the specs online. With a N100 mini pc, I’m not so sure if that’s a big step up from your current setup… I don’t think they have more internal harddrive ports or slots for GPUs than your current laptop.
Software: https://github.com/awesome-selfhosted/awesome-selfhosted
Guide: https://github.com/mikeroyal/Self-Hosting-Guide
As a beginner you might want to start out with one of the all-in-one turnkey operating systems like yunohost.org , dietPi.com or unRaid or a bunch of others (see the awesome-selfhosted list)