Can I stack a dryer on top of it?

Yes. It is designed as the base of a stacked pair, but the dryer on top should be the matching Equator model, and a stacking kit is normally needed. Check that the dryer is rated for stacking before you buy.

Does it need a special electrical outlet?

No. It runs on 110V, the same as a normal wall outlet, so it does not need the 240V circuit a full-size electric dryer uses. That is the main reason it suits apartments and older buildings.

How much can it wash in one load?

It is a compact machine, so expect noticeably smaller loads than a full-size front loader. For a one- or two-person household that is usually fine; for a family, plan on more loads per week.

Can I use it without stacking a dryer on top?

Yes. It is freestanding and works as a standalone washer. Stacking is optional and mainly a way to save floor space.

Is it good for a small apartment?

It is one of the better fits for a small apartment because of the narrow stacked footprint and the standard outlet. The trade-off is smaller loads and longer cycles than a full-size machine.