Does the KffKff Full-Size Canopy Bed Frame include a mattress?

No. It is a bed frame only, so you supply a full-size mattress and box spring or platform support as the frame requires.

Can I hang curtains or a mosquito net on it?

The four corner posts form a canopy, so curtains or a net can be hung from the top rails. Check the frame's height and rail layout before buying fabric.

What does the built-in storage hold?

The listing describes built-in storage but does not detail its size or placement. Confirm with the seller what the storage section holds before you rely on it for bedding.

Is it sturdy enough for adults?

It is a steel frame, which is generally rigid and resistant to warping. Check the seller's stated weight capacity for the full-size frame.

How does it compare with a wood canopy bed?

Steel is lighter, cheaper to build and less prone to warping, but it looks more industrial and usually has no headboard. A wood canopy bed gives a warmer look at a higher weight and cost.