PLC Programming to run a Heat Pump and Air Handler

So, I have had many issues with my heat pump/AC/Air Handler system. I happen to have a micrologix 820 I think, a vfd and a 3 phase motor. I would like to make sure my program for control includes all the elements I need. So the circuit boards replacing them, as well as the multispeed motor are astronomical in price now.
My understanding as follows. Outdoor/Compressor unit is always in heating mode, the valve, unless you call for cooling. So Tstat calling for heat, or cooling will start the compressor and cooling fan. At some predetermined time period, the valve reverses to de-ice. What is that time period set for approximately ? There should be a high and low pressure switch to stop the compressor to prevent damage. I may bring a parallel signal into my plc for monitoring. So I program 1 relay out to start the fan and compressor outside. This will be in series with the pressure switches. Fan on will be if compressor is on. I have a pid to control my fan inside. It's an 1150 rmp motor. What should I use as Minimum speed ? Any thing you know that I am missing plz feel free to add
You appear to be missing a 'Process Description' !

Control Engineers sometimes are expected to use a magic wand...
Even if you have an idea of the process you can 'second guess' parameters but unwise if it does not then work as designed.

Can you write a Functional [Control] Description of what you know ?
If not then you need some form of, however brief, a Process Description.
Well, I do not have that, which is why I am posting here. I have a general idea on the process, but I am not familiar much with HVAC control. If some1 is, please reply
Defrost mode on a heat pump stops the outdoor condenser fan and switches the reversing valve to cooling mode (steal heat from inside house to heat/de-ice the outdoor coil). Triggering this sequence is generally based on outdoor air temp and a coil frost sensor. At the same time the indoor aux electric heat strips are brought on to continue to heat the occupied space.

These control boards are cheap and readily available. As a HVAC vendor I would never take a unit over that has these OEM boards. Suggest you don't either, any unit warranty left would be gone.