30+ year old GFA furnace, hoping to have it squeak through one more
winter. New to this home, old owner wasn't very good about routine
maintenance. Replaced the furnace filter right away; it was clogged
with dog hair and dust...

At the pre-sale home inspection, the inspector noted that the
temperature in the plenum was running high. I don't have the exact
figure, but the registers in the room directly above the furnace get
REALLY hot to the touch, way too hot to me. My impression is that the
blower isn't really blowing all that well, either.

Questions:
1) could there be dirt and crap further up in the system (A-coil??)
causing air flow restriction and the high temps at the plenum and near
registers? How to check? How to clean?

2) Calling in the HVAC guy is on the to-do list, but they're really
booked up right now. What minor stuff can we do (cleaning, examining)
until the HVAC guy comes to do the winter inspection/tune-up??

3) Is it dangerous to have such high plenum temp? Furnace is not short
cycling, or acting wacky in any other ways..