Synology’s telegraphed moves toward a contained ecosystem and seemingly vertical integration are certain to rankle some of its biggest fans, who likely enjoy doing their own system building, shopping, and assembly for the perfect amount of storage. “Pro-sumers,” homelab enthusiasts, and those with just a lot of stuff to store at home, or in a small business, previously had a good reason to buy one Synology device every so many years, then stick into them whatever drives they happened to have or acquired at their desired prices. Synology’s stated needs for efficient support of drive arrays may be more defensible at the enterprise level, but as it gets closer to the home level, it suggests a different kind of optimization.
Really depends on what you want out of the system, what you can spend and how much time you want to spend on it.
My old z390 itx system has a 16x PCIE to 4x m.2 card - leveraging an m.2 to 5x SATA adaptor with the built in SATA adaptors has given it plenty of space.
Considering I can grab m.2 to 6 SATA adaptors and fill the remainder of the slots that’s a decent chunk of drives from a single PCIE x16 slot.
Software is another kettle of fish and a good way to timesink, I’d rather not give too much of my personal experience as there are so many ways to skin that cat.