Prior to having solar panels fitted in 2017 I regularly went three or four days off-grid. I never really looked at battery percentages, as soon as voltage drops below a certain level so stuff like the fridge will no longer work and warm white wine is a big enough alarm bell to tell me my batteries are critically low.
My previous vehicle was a 2013 T5, it had an unrelated electrical fault, the batteries were tested when the fault was rectified and found to be in top condition so my less than diligent power management did not damage anything.
As for heating, remarkably effective, a lovely piece of kit, I did not buy a Cali to be cold so if justified it's on all night, all day and all the time until I don't need it. It uses power on start up, then settles down once operational to using not very much, so leaving it on all the time is probably more battery efficient than switching it on and off.