Manuel 3 answers for two questions:
First on the cooling fan coming on sometimes, This can happen even if you are not plugged into shore power the fan runs on 12 volts. which can come as easily from the battery as from the converter, and is controlled by a thermostat.. SO the heat of the sun casn cause it to come on if the compartment it is mounted in gets hot.
As to "is it a 3 stage smart charger" First reading of the link you provided, I do not think so, appears to be single stage,, However digging still More to follow in the next paragraph, Please stand by.
Doing additional research, downloading a couple of documents from Attwood, you have shown us a combined power distribution panel/converter. It still appears to be single stage but with better regulation than the Magnatek.. I do not think it will boil the batteries completly dry, Nor will it charge them to full capacity. Upgrading the converter module might be a task for your "Down the road" list.
I personally, do not like "All in one" power panel/converter set ups. I mean with mine where the power panels and the converter are a good 10 feet from each other.. Way easier to service one or the other.
Home is where I park it!