I don't think you can beat the comfort that cast iron will give you when it is really cold out, like you experience in winter. With forced air heating, because the heat is carried on the air, these systems it will always feel breezy and drafty. With the cast iron radiators you not only get great convection heating but get all that radiation as well. Forced air cannot begin to compete in the comfort or price of hot water. Here is clue; In Europe where energy cost three times as much as it does here in the states you cannot find a home that is not heated with circulating hot water. Also when you get north of North Dakota into Canada where air conditioning in not nearly so much in demand, 90% of homes are heated with a boiler and circulating hot water. In Montana, in the Dakotas, the upper mid-west and the north-east, circulating hot water and steam are use far, far more more that forced air. They do this for two reasons; one is comfort the other is cost.
Use a 20A breaker and 12 AWG (or larger) wiring.
I read through the installation manual, which was surprisingly bereft of meaningful electrical information. Regardless, the MCA is the required Minimum Circuit Ampacity, meaning your circuit needs to be sized appropriately for at least that amperage. The 24kBTU unit has an MCA of 15, so you'd need a circuit capable of supplying at least 15A.
Because this is HVAC equipment, a 14 AWG circuit and 15A breaker is insufficiently sized. This is a continuous load, so you're only allowed to size to 80% of the rated ampacity, and the next larger size is 12 AWG and 20A.The Max Fuse simply states that the maximum size of the OCPD should not be larger than 25A.
HACR is likely to be listed on your breaker, but it's no longer required. Neither the NEC nor UL requires it to be labeled anymore, so don't stress over that.
You can do what others have suggested and use a larger ampacity circuit with an appropriately fused disconnect at the unit, but your circuit would be needlessly oversized.
To directly address your questions, the labels indicate electrical specifications for the unit, and if the instructions only show the indoor unit directly connected to the outdoor unit, then the outdoor unit should provide for any protection the indoor unit requires. The circuit only needs to supply enough current for the unit and not allow more current than the maximum rating.
And no, you don't need to use fuses over breakers.
Best Answer
It is legally mandated, and part of the National Electrical Code (NFPA70). NEC is adopted across most of the US.
It's largely a safety precaution to ensure the power is off if someone is servicing the unit.
If your breaker panel is 20' away and within sight of the unit, it's probably acceptable as a disconnect means but of course your AHJ (inspector) will have to agree. If you can't see it, you'll have to put in a separate disconnecting means.