Clean Filtered Air

Long story short, my daughter got diagnosed with Leukemia (B-ALL type) recently. Treatment is 2-3 years long mostly at home and she'll be more susceptible to viral/bacterial infections and mold issues. To try and control as much of the variables as I can, I'd like to make some HVAC improvements that can help keep the air clean and humidity controlled. I have two HVAC systems; one in attic for upstairs and one in basement the has vents to both 1st floor and 2nd floor. I've come up with the following in order of importance:

1. Upgrade air filters to MERV 13 (Upstairs already has 4" filter grille and I'm getting 4" filter cabinet installed on downstairs system; contractor will do static testing to ensure things are acceptable)
2. Whole house HEPA filtration on downstairs system (I think this will be setup as a "bypass" type system so it doesn't put strain on the blower")
3. Winter humidity already controlled by Aprilaire bypass humidifier (had issues with this last season but found out the saddle-valve was clogged and had a T-valve with a 1/4 turn shut off installed instead and now it flows well; if it still can't maintain, I'll replace with a steam humidifier)
4. Install ventilating dehumidifier for should season and high humidity summer days (this will have to wait due to finances)

I thought about installing UVC lamps in the coil area, but was told that this doesn't disinfect air; just the coils and only the side of the coils the light is on. So I'm not going to install UVC lamps. I'm going to mitigate this by having the HVAC folks clean and disenfect the coils regularly. Do you think I should get them cleaned/disinfected 1-time per year or 2-times per year? If 1-time per year, beginning or end of cooling season?

Did I miss anything? Should priority be changed on anything?

Thanks!

source https://hvac-talk.com/vbb/threads/2241884-Clean-Filtered-Air?goto=newpost