The duct kit is 8" duct. Not sure of cost in your area for fire damper.
This our smallest unit. I am sure it will dramatically improve the humidity level in your basement. If you want whole house humidity control of 50%Rh, the Santa FE advance may be a better choice.
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"