If you have resistance style electric heat you will see a dramatic electric bill reduction. If you heat with oil or propane your electric bill will go up, but the savings will exceed the fuel costs you typically pay.
Heat pumps need to defrost when ice forms on your outdoor unit on colder days from condensate in the air. Your unit will automatically switch to cooling mode to do this. Although alarming at first, this is perfectly normal operation.
Fujitsu warranties the product for their Elite contractors for 12 years, which means they will obviously last longer if properly installed and maintained.
Filters should be checked and cleaned as needed. Everyones home is different but as a rule at least every two months.
Yes, heat pumps collect a lot of dust and it will build up over time on the indoor and outdoor coils. This buildup can lessen the ability for the unit to operate properly and efficiently.
This of course depends on the installation but as little as 4-5 hours for a single zone system.