Depending on bank size and battery chemistry vs charger Amps, best to put all charge sources including alternator to the bigger House bank, and use the DCDC charger to feed the smaller Reserve/starter.
Not recommended. The Alternator should stay charging the starter battery. The alternator is designed to recharge a starting battery.
The B-B charger will not load the starter battery(actually the alternator through the battery cables) until it senses the starter battery at full charge.
If you reverse the b-b set up you could well get the situation where the house bank never gets full charge (short drive times) and consequently the B-B charger does not engage to charge the second bank, in this case the starter battery.
dwh must be on MPPT overload.:costumed-smiley-007
Battery to battery charger boosts voltage. A buck lowers voltage.
You can't use a B2B and an ACR together. It creates a feedback loop. The output of the B2B gets looped back around to its input through the ACR.
If you exchange your Cole Hersee with Ctek D250, & its output serves both house batteries, It will work if you can live with Ctek 20amp limit. (and its insane pricetag !!)
But if you plan to use front house battery to supply the Ctek what then charges the rear battery.
There are a couple scenarios to define.
1, If the two house batteries are separate "house systems" this works. (But 20amp max.to rear battery...)
2, If its to work as 2 house batteries combined. One will need a method to bypass Ctek combining the house batteries, What sort of renders Ctek moot except for its neat voltage boost charging feature.
No problems then. Just use Ctek as would any other isolator. Its input supply coming direct from the alternator.