There are spectrums of how much "business" I do with a coworker. If it's another person that works on the same floor or in the same building as me but whom I don't work with directly, then I don't really see any good reason to exclude them.

IMO being professional is more about how you handle the situation if the relationship goes south or never gets off the ground. PDA in the workplace is also unprofessional, obviously. But asking someone out? Doesn't seem unprofessional tbh.