I recently took over a 20 year old vehicle from the parents which they bought new. The cabin filter was in the same condition. After a new filter, I no longer need the blower motor nearly as much as the vehicle's speed is enough to move air through the vents now that the old plugged filter is in the landfill. Also decided to go with a charcoal layered filter which eliminated the musky odor after a few thousand miles. Well, Ok, I also had to use one of those scented bombs to help get rid of the odor, but at least nobody is complaining about the smell any more.
For the battery, Noco is certainly a nice product. Am using one for my LiFePO4 battery packs.
For a few $$ more, might consider something like a 5 - 10W solar charger as there is less wiring to mess with. Only downside to the solar charger is forgetting to unplug the thing before starting the engine as the array does not like back-feeding. These devices usually come with a LED inline with the positive lead which also acts as a diode to prevent back-feeding, but I like to keep my risk factors at zero instead of low. I am using a 5W solar charger on the Ferd diesel with good results from when it sits for a while.