Windows should be as high as possible in order to allow natural light to penetrate as far as possible into the room. Doors can be lower and usually are. The height of a ceiling should not be a matter of looks but support the overall design of the house and provide opportunities for interior light. An 8-4 height is surprisingly better than 8 ft. and 9 ft is sufficient for almost any house in my opinion.

I'm one of those who prefer window heads and door heads to align. To me, it looks much more thought out and less random.

I agree about the importance of window heads being high in order to allow more natural light in the interiors. If you live in a hot, humid zone, however, you may want to consider exterior shading devices for summer sun angles.

A 20 X 25 room is rather large. I assume there is no occupied second floor above the space (if there is, then stairs and other considerations quickly come into play in evaluating ceiling heights).

Ceiling heights, however, are often best considered by use of the space, rather than having multiple uses all clustered under one common ceiling plane. For example, a space for quiet reading and listening to music may be much more intimate than a space for large social groups and entertaining/dining which may have a higher ceiling plane to increase the visual/emotional size of the space.

You don't define what uses are included in the room, so the only way to respond is to consider ceiling heights that make overall pleasing proportions, when considered with room length and width. I'd probably start by looking at a ceiling plane at around 10' for a room that size. That would also allow for 8' window and door heads.

You could probably go as high as 12' if you are looking for volume; 8' is too low, IMO.

Good luck on your project.