The two stage PD 14.6v lithium converter/charger should automatically drop down to a 13.6v - 13.8v float after a few hours of charge time (time varies due to SOC). Not sure if the PD Charge Wizard works on the new 2-stage PD lithium chargers. If they do, you have the option to manually force it down to the lower float voltage with the Charge Wizard.
As for proper wire/cable size. What will be/is the length of the wire/cable run from the converter(s), dc to dc charger, etc. to the batteries? Here is an
online Voltage Drop Calculator you can use that might be helpful (click on the Estimated Resistance tab). Ideally, you should strive for a 2-3% voltage drop under max load.