Is 8 GB of RAM enough for this all-in-one?

It is fine for browsing, email, documents and streaming. With many browser tabs, large spreadsheets or photo editing open at once, it will slow down sooner than a 16 GB machine.

Can I upgrade the RAM or storage later?

All-in-ones are harder to open than towers, and HP's service documentation should be checked for the specific model. Plan on the 8 GB and 512 GB as configured rather than counting on easy upgrades.

Only light or older titles at reduced settings. The Ryzen 7 7730U uses integrated Radeon graphics, so modern games and 3D work need a desktop with a dedicated graphics card.

Does the 27-inch screen work well for video calls?

Yes. The large Full HD panel gives plenty of room for call windows and shared documents, and the built-in webcam and speakers keep the desk free of extra accessories.

How does it compare with a tower plus a monitor?

You get the same desk space savings and fewer cables, but less flexibility. A tower lets you swap the monitor, add a graphics card and upgrade memory freely; this unit does not.