Is this Bosch BPHA-60RCB-M16S unit wired correctly to take full advantage of the multistage indoor fan speed?

I recently had an inverter-driven Bosch BPHA-60RCB-M16S (Bosch IDP Plus) installed (replaced a single-stage package system from 2012 or so). The house was built in the early 2000s (this is the third unit for the house, but we only bought the house a year ago).

The salesperson (35+ years experience, former tech moved to sales) was very knowledgeable when he sold me on the Bosch unit, but the HVAC techs that did the install did not give me a ton (pun intended) of confidence that they knew what they were doing. I would ask basic questions about the unit operation, and they seemed confused. Inverter-driven units are not common here in Tennessee, from my understanding, so that makes me particularly wary about trusting that the job is done right.

• Compressor: I understand this unit uses the refrigerant temperature (or pressure?) to control the variable compressor (rather than relying on a proprietary linked thermostat), so that part I am not as worried about. (correct me if I should be)

• Blower(indoor fan): Unit is capable of up to 4-stage indoor fan control. Is the selection of fan speed controlled by the thermostat or the unit? One of the main reasons for getting this unit was to increase runtimes at lower flow rates for better air distribution and quieter operation. Below is a link to the wiring behind the thermostat.

• Thermostat Wiring: Honeywell FocusPRO S200 [https://imgur.com/a/mfuCNrC]

• Aux Heat Temp: The unit has lower outdoor temp operation than typical heat pumps. Our typical outside low temp in the winter is ~20F, but can for short bursts get down to -1F once or twice a winter. The closest ASHRAE weather data location is Clarksville Outlaw Field Airport, TN, USA. What outdoor temp should the aux heat strips be set to turn on? (trying to maximize efficiency, I understand the defrost cycle will use the aux strips as needed)

• Unit Sizing: The unit is a 5-ton package (manufacturer has 3 and 5 ton models) unit that is selectable downwards from 5 tons down to 3.5 tons (maybe lower) using DIP switches. For my house, 3.5 tons is what the unit was there before. Is there anyway for me to verify that the unit was downrated to 3.5 tons without pulling off the covers on the unit outside?

Note: I am a mechanical engineer, but HVAC is not my speciality; I know just enough to be dangerous and a worrier.