I have an 8 / 256 M2 Mini that I routinely run Office (several products open at the same time), a couple of browsers (often open at the same time and with multiple tabs open on each), use Zoom / FaceTime, do basic photo and video manipulation / editing, run a few peripherals - like external drives and printers - and do the occasional video streaming. And everything seems fine.
I rarely see the beachball, and then, when I do, its more often than not an Apple app temporarily misbehaving. Would more RAM solve that? Probably not.
Now granted, I do keep the device 'clean' over and above the default Apple management (I use CleanMyMac X, but the free Onyx is a good bet, too), and while I understand the popularity of more RAM (as noted), the combo of new chips and SSD covers a lot of bottlenecks older technology created. And while you'll pay a premium for more more RAM, its unikely you'll ever realize that expense back when / if you do a trade-in / sell it down the line.
Now, if you're into some fairly complex spreadsheets, doing CAD or 3D graphics and animations, or are running multiple OSs or are blasting thru some of the games being ported to Mac, more RAM is probably a given, but buying more RAM to 'future-proof' your Mac is a mug's game. Heck, I still have my 'old' 2017 MacBook Intel Air (8 / 256) I keep around for work / travel, and it sill runs the (updated) software I need it to do without beachballs.
Oh, and short of some deals at retailers (like Costco), you might want to take a look at Apple's own online Reburb site. You may find the Mini you are looking for at a price you can afford. All items come with same warranties as new (plus available for AppleCare) and are shipped free. Stock always changing.