Is this door a single slab or a complete prehung unit?

It is prehung, so the frame and door come together as one unit. That saves time on site compared with building a frame around a bare slab.

Will a 60 by 96 inch door fit a standard opening?

No. That is a wide, full-height double-door size. Measure your rough opening first; most standard single entryways are much narrower and shorter.

Does the glass hurt energy efficiency?

A large glazed panel loses more heat than a solid insulated door. In cold climates, check the glass specification and consider a low-emissivity or insulated glazing option.

How does it compare with a solid steel entry door?

It gives much more light and a more open look, but a solid steel door offers better privacy, security and thermal performance. Choose based on how much daylight you want at the entrance.

Does the aluminum frame need maintenance?

Aluminum is durable and does not rot, but the finish should be cleaned periodically. In coastal or harsh climates, check that the coating is rated for the exposure.