Some similarities here FF.
I bought the boat in 2010. It had/needs dual purpose type 8Ds, both 5yrs old, no solar, and not looked after. I replaced one 8D, saved one for a year, the genset battery for 2.5 yrs, using a desulphating agent(snake oil?), and adding solar of 90w per main battery, and 25w for genset batt. The 8Ds seem to be doing ok, I`m not sure monthly equalizing was helping, it`s off for now, and I`m suspicious about the separators condition. I`ll get new ones if I have to, but fitting 54kg batts is a PIA. So what life I will get is unclear. I replaced the genset 150ah start batt with a sealed tractor/boat one, I may get the 8D/200ah version of it for the mains if I replace, but not yet, I was hoping for 5 years.
We have a eutectic fridge & freezer. Cruising, that keeps fridges off the batteries, I run the genset early and late for the eutectics, and can charge batts, as needed, same time. For single overnights the batts are up to the job of running a 12v fridge, especially if the day was sunny and fed the panels well. Our stove is propane/LPG, we have an electric frypan/roaster, electric kettle, small espresso coffee machine all needing 240v,via the genset, and a small inverter for TV (65w), and other small things.
It`s interesting how people work out their own needs in the context of their own boat. There is usually a way of making things work. I envy your 6-8 years of battery life, I think it`s possible for us, my 8Ds need watching for now, I don`t think the equalizing has been good for them. I`m sure solar is the key to long life, packing in that last 20% they otherwise don`t get, we are on a mooring, not a marina, quite common here.