Real world dehumidifier capacity is much lower than rated.

Without knowing air infiltration, moisture produced by people, moisture from foundation, can't accurately size.

You should avoid the cheapo plug in chinese dehumidifiers - they're bad quality and short cycle due to the sensor being too close to the coil and being poorly designed. Estimated lifespan - just through the warranty period.
The manufacturers of the crappy retail dehumidifiers also don't publish real world performance in different conditions.

Go commercial grade and consult a commercial hvac contractor who can check the building and properly size.

 

How do I calculate for unit size myself. We will be getting a blower door test after improvements. How can we do the calculations and size the unit ourselves? I know the technical language is shrouded in esoteric terms, but how can one DIY calculate for HVAC needs?

 

How is the building cooled/heated? Maybe get the next to the biggest dehumidifier installed in the duct work. What % are you trying to achieve?

Your drawing is helpful but with out measurements of current and after I do not believe there is an easy answer.

What is the point of a blower test? What standard are you trying to achieve?

What ever you do, make sure the units are piped to a drain so no one has to empty them.

I worked at a University and we had an theater which could seat ~3100 people.
We would turn the ac on before a show and try to get the building to 55F. Usually got close. The units made so much noise that we had to slow the fans down to a crawl during shows. Building was usually over 80F when the show was over.

 

How is the building cooled/heated? Maybe get the next to the biggest dehumidifier installed in the duct work. What % are you trying to achieve?

Your drawing is helpful but with out measurements of current and after I do not believe there is an easy answer.

What is the point of a blower test? What standard are you trying to achieve?

What ever you do, make sure the units are piped to a drain so no one has to empty them.

I worked at a University and we had an theater which could seat ~3100 people.
We would turn the ac on before a show and try to get the building to 55F. Usually got close. The units made so much noise that we had to slow the fans down to a crawl during shows. Building was usually over 80F when the show was over.

Blower door test is to find leaks and make sure it is very high. Target? I don't know. If it is 7ach, we need to seal more. If it is 4 ach we will probably call it good.

An inline dehumidifier, is more expense, and is additional expense when time to change it out. so we will avoid that.

It is currently heated/cooled with heat pumps.

What does an HVAC guy do? The few I have used when building 3 houses only guessed a size as I did not see any real testing done. I have also seen them replace with a same size unit. I imagine in areas where energy codes are more stringent, the work is done to better practices.

Surely it is only esoteric knowledge, and not rocket science how to size a unit. If I can't get help here, I will reach out to some HVAC people and ask them how they will come up with a solution before hiring them.