Is the HP EliteOne 840 good for gaming?

No. It uses Intel integrated graphics, not a dedicated GPU, so it suits office work, browsing and video, not modern games.

Can I upgrade the RAM or storage?

The listing shows 16 GB DDR4 and a 512 GB SSD with one slot. All-in-ones are harder to open than towers, so check HP's service manual before planning upgrades.

Does it come with a monitor?

Yes. The 23.8-inch display is built into the unit, so no separate monitor is needed.

Expect the all-in-one unit, a power adapter and cable, and a keyboard and mouse in most retail bundles. Confirm the bundle with the store before ordering.

Office workers, reception desks and home users who want one tidy unit for documents, email, web and video calls.

Is this a good value for the money?

It is positioned as a premium business machine, but it carries a high price for an i5 all-in-one with 16 GB RAM. Compare against similar business all-in-ones before buying.