“Sufficient “ is entirely your decision, based on your needs, your usage trends (and app and macOS trends), and your budget.
The amount of storage purchased is a tradeoff with the amount of storage management effort required later.
I wouldn’t personally select a 256 GB Mac, as I would not fit. I have whole lot of data, and a whole lot of photos and video, and would prefer to avoid deleting chunks of data, and scattering the rest around onto add-on storage.
Other folks can fit into 256 GB just fine. But it can be more work, and it’ll mean shuffling files around, and deleting data.
As examples of some bigger usage requirements encountered, macOS 12 required 26 to 44 GB to upgrade, while macOS 13 requires 25 GB, and macOS 14 wants around 14 GB.
You’ll also want external storage of two or three times the internal storage capacity too, for Time Machine backups. Hard disk storage works fine, here. Why added storage? The only way to mark data as being valuable is with backups.