Is the Core Ultra 9 285K good for CAD and 3D work?

Yes. The 285K is a high-core-count desktop CPU that handles CAD modeling, rendering, and compiling well. Heavy GPU rendering still needs a discrete graphics card, which this configuration does not include.

Can I add a graphics card later?

The small form factor limits you to low-profile or compact cards and depends on the power supply's wattage and connectors. Check the PSU rating and slot clearance before buying a GPU.

How much memory can it take?

It ships with 32GB, which is ample for most engineering and content work. The platform supports more, so you can expand if your workloads grow, subject to the slots available.

Is this the same as a consumer HP desktop?

No. The Z2 line is a business workstation with ISV certifications, manageability tools, and a serviceable chassis. Consumer desktops typically offer less expansion control and fewer security features.

What comes in the box?

The desktop unit with its power supply and standard accessories. A keyboard and mouse are not guaranteed, so confirm with the seller if you need them.

Is it good for gaming?

It can run games on integrated graphics at modest settings, but it is not a gaming PC. For serious gaming you would add a discrete GPU, which the small chassis constrains.