Thanks for the concern everyone!
In the couple of months I’ve been aboard so far (it’s not a widebeam by the way, I’m not sure where that idea came from) I’ve been on the move a lot so the alternator alone has been more than sufficient; obviously this’ll change when things get more sedate and as has rightly been pointed out the best way for me to figure this out is to see what happens and make appropriate adjustments.
I’m not a heavy user of electricity, mostly just a few lights and sometimes the fridge if there’s something in it to keep cool and I have the stove going. A television and occasional use of the washing machine, plus charging phone batteries, would all be nice but I have options ashore for sorting those problems. I can certainly adjust my use to fit the availability, and if it turns out to be necessary, there’s options to explore like more panels, more batteries, a generator, even a wind turbine (although I gather that might be a waste of time).
The 2000W Sunshine inverter that draws about an Amp on standby is far more than I’d need; if what I’ve read on the topic is right, higher Wattage inverters draw more power on standby, and by my very rough estimates I’m thinking a 500W inverter would do me fine.
Regarding battery monitoring, I have a solar controller (EPever Tracer 30A MPPT) awaiting installation that I believe will provide the numbers to make calculations upon; finances being what they are I’m assembling the solar system bit by bit, intending to get the first panel in a few weeks, and maybe another the following month.
Apologies for not being clear; what I was getting at was whether running equivalent appliances built natively for 12V or 240V (via inverter) would differ significantly in the amount they drain the battery bank.
Thanks again everyone!