Dead Filter: This has been XPosted

I went to a movie at around 9:30 PM. My fish tank is near our door (a
sin, I know, but anyway...). When I walked in a bit after midnight, I
immediately noticed that the filter wasn't running.

I'm assuming that it was running when I left--I believe I would have
noticed, and anyway, I think I recall seeing water movement when I was
glancing over there earlier. I remember because upon seeing the
movement, I checked to make sure my loach wasn't bothering his arch
nemesis (a neon) again.

Anyway, so that means that most likely, the filter was off for three
hours or less. The tank has a few plants in it. The water temperature
and whatnot is fine, so it's just the filter that broke.

Anyway, we immediately removed the old filter (though some water
spilled out of it) and turned on the airstone. After a quick trip to
the 24hour walmart for a new filter (Tetra Whisper, anyone used it? I
haven't heard much and our normal brand is aquaclear, but we didn't
have much choice and will check the LFS tomorrow) we now have a
complete tank again. I'm worried about the following:

a) The bacteria. I'm worried the ones in the tank died.
b) The bacteria. I'm worried that by changing the filter stages all at
once, there's going to be an ammonia spike
c) the bacteria. I'm worried about the crap water that spilled out of
the old filter when I removed it.

Anyone have any words of wisdom? We did test the water and the
parameters were fine, but I'm not convinced that the damage would show
up so quickly. Fish seem to be acting normally.

Also, should I do a water change tomorrow, or not?

(XPosted at Freshwater Fish Tanks)