Is the 27-inch 1080p screen sharp enough?

It is fine for video, browsing and office work at normal viewing distance. Text is noticeably less crisp than on a 24-inch 1080p screen or a 27-inch QHD panel, so it is a weak choice for heavy reading or design work.

Can I upgrade the RAM or storage later?

All-in-ones are harder to open than towers, and ASUS does not position the V400 for user upgrades. Buy the 16 GB and 1 TB configuration you need up front rather than planning to add parts.

Does it handle gaming?

Only lightly. The integrated graphics run older and casual titles at low settings, but modern 3D games will struggle. A desktop with a dedicated graphics card suits gaming better.

Is the touchscreen useful on a desktop?

Yes for kiosk, reception, family and media use, where tapping is quicker than reaching for a mouse. For long typing sessions most people still use a keyboard and mouse.

What do I need to add?

A keyboard and mouse if you do not already have them, since the unit is the screen and PC in one. Wi-Fi 6E is built in, so no network cable is required.

How does it compare with a tower plus monitor?

It saves desk space and cables, and the touchscreen is uncommon on budget towers. A tower gives sharper displays, easier repairs and proper graphics upgrades.