I've considered getting a mac mini with decently specced CPU/GPU and plenty of RAM and then just attaching a big SSD via thunderbolt. Probably a lot cheaper than maxing out the internal SSD and I don't think it will be that horrible. My main use case would be dealing with photos, maybe X-plane, and some videos. I might buy some games as well but it's not my core use case. It seems the Apple store is slowly filling up with a decent selection of ported games. I gladly pay the Apple tax to never deal with Windows again. I actually have a linux laptop running Steam. The hardware is just really crap and I keep longing for my macbook whenever I have to use it. Actually typing on this thing right now as I'm traveling and I left my work M4 Max mac book at home (it's a bit of a beast to lug around on vacation). The mini would probably be hooked up to a TV so I can watch stuff via Firefox and use a sane ad blocker and UI rather than dealing with whatever crap tastic shit comes with modern smart TVs.
So a reasonably beefy mac mini would basically be my entertainment center and double as a home PC with a ginormous 4K screen. I have considered getting some AMD equivalent with Arch Linux. Still on the fence about that. But either way, external USB-C for storage seems fine.
More than once I’ve had, say, Photos complain that it couldn’t find its library because I have apps relaunch on startup, my library has been moved to external storage, and the drive was not ready yet.
Also there’s no guarantee, at least naively, that what was /dev/disk4 on the last boot will be /dev/disk4 on this boot. Normally not necessarily an issue, but if you care about actual drive devices vs volume names, it can be an issue. (And there well be some low level config file wizardry to fix that issue, I just haven’t bothered to research it.)
I'm sure there are cases where you really do care about speeds >3GB/s (and USB-4, the port on the mac, should max out at ~5 which is still marginally lower than the internal one). But I doubt they are common. It's hard to process most data in a meaningful way that fast.