Austin Air A250B1 HealthMate Plus Junior Air Purifier

Yes. You can easily roll them around.

Plus as the activated charcoal for gases and formaldehyde

The larger units when running on high are noisy. Low and medium not too bad.

It mainly depends on how dirty is the air in your place. I replaced mine (the main expensive filter) after 3 years. But I think I could easily have stretch out to 4+ yrs. As far as the outer dust filter, I replace it annually or just wash and use. There was no instructions on that.

Yes, you must restrict the airspace that it purifies.