With some time and money to research, plan and renovate, it will become quite a comfortable van. Still not ideal but good enough.
Not sure exactly how to deal with batteries. My idea was to buy three bulky powerbanks to keep a phone and iPad charged at all times and charge the powerbanks and a laptop at a caravan park or local library. This has the downside of needing to travel long distances when it's cooler or the food in the fridge will spoil.
Tall enough to need a longer van to lay down in. I won't be able to stand up inside.
This is a concern which I'll struggle to deal with. My only idea so far is to keep a tent in the van. My other main concern is how to safely store two gas bottles and three powerbanks. If someone hits me there could be an explosion.
Australia never gets as cold as Norway. Sleeping in a hammock is something I'll only do if my van is at the mechanic because I don't feel safe sleeping without four solid walls around me.
"solid walls"
Show me a locked van and in a few minutes I will show you the inside of it, I am not that good at such things either -- show it to the people that taught me such things and 30 seconds on a bad day (one of the more amusing stories there was one guy's in laws locked the keys in the van, he went round there, his wife rang the bell, by the time they made it to the door to answer it, this being a small UK house and said in laws still spry, he was standing there with the keys).
If you are also concerned about creepy crawlies (you did say Australia after all) then... yeah.
Re gas bottles.
Modern ones are fairly well rated not to explode, as are consumer power banks.
Dual batteries is something any vaguely good mechanic will be able to handle (though it gets far cheaper to do it yourself -- isolation switch, tap from the alternator and run a fat old wire hopefully not through the fire wall*, possibly a charge management, few deep cycle batteries, said pure sine wave inverter, enough stuff to hold it all down and isolate electricals). Builders, miners, weekend campers, nature photographers... have such things installed all the time and if you only want it to charge a few things (by the way solar panels do well for this if you can coat a part of the roof).
It tends to only get fun if you want to run microwaves, kettles and tools themselves from it. If you wanted to get one of those big boy house grade power banks then some of that comes as one.
Get some kind of camping ground, farmer's field to stay in, friend's driveway or something you can have shore power from and you are laughing (though also likely need to spend a tiny sum to get the suitable power leads in the case of most camp grounds).
*quite a few van models have batteries under the seat in the cab or even in the back already these days.
Electrics might not be your thing which is fair enough, however you do want to be able to check oil, probably be able to change it in a pinch, check other fluids, check tyres for tread, wear, uneven wear and such. Might not also be the worst plan to have a cheap code reader either.
Re keeping food fresh. Those peltier cool boxes do very well (though they are less good at getting temps down so might have to sacrifice some space and go buy a bag of ice every so often), and gas bottle fridges (as in powered by gas bottle, called absorption cool boxes if you want the more technical name) are a thing still as well.
I am usually more concerned with heating food -- gas, charcoal bbqs, gel fuels... whatever do get kind of expensive when you are out for more than a weekend or one off or making the odd cup of tea. Solar ovens
https://www.treehugger.com/best-solar-ovens-5120148 being wonderful things in this and that is in the UK, somewhere that actually gets some sun and you are laughing.
