There are several ways to do an electrical system.
The simplest way is to buy a power station and plug everything into it. These units combine all the components (inverter, battery, charge controller, outlets, fuses, wiring etc.) of an electrical system in a compact, portable package. Many power stations come with factory or third party warranties. Power stations are sufficient for most simple to medium complexity van builds. Mid sized power stations are capable of running a fridge and microwave.
Power stations by unknown Chinese brands are starting to hit the market and prices are dropping precipitously. With 4 year warranties available from Asurion, I wouldn't hesitate to try something like these:
https://www.amazon.com/Portable-Sta...-garden&sprefix=power+stations,aps,363&sr=1-3
https://www.amazon.com/dp/B09NZP9Z2...KAX396WM&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it
At the other end of the spectrum is a completely self built system assembled with individually selected components. With this complexity comes the flexibility to cater to specific/specialized needs, like a high amperage appliance. This approach takes a fair bit of knowledge and a willingness to accept responsibility and risk. Should you wish to go this route, YT vlogger Explorist Life has a couple of dozen videos dedicated to electrical systems in vans. There used to be a big difference in price between DIY electrical systems vs power stations, but nowadays the delta is minimal.
Somewhere in the middle is a hybrid system that tries to utilize the advantages and minimize the disadvantages of the above approaches. Permanently installed accessories (eg. rooftop AC, fan, heater, lights, USB ports) are hard wired to a distribution box, which is connected to a power station. This gives flexibility in the placement of accessories while letting the power station do the heavy lifting.
There are multiple ways of indirectly charging via alternator.
Almost all power stations can be charged via a vehicle's cigarette lighter. Typically this maxes out at 8-10A (96-120W). The VS30 cigarette ports are regulated to 10A.
Some vehicles (like the Transit) have built in OEM inverters capable of delivering 400W. This is sufficient for 110V charging of some power stations (like the Bluettti AC200P).
It is possible to charge a power station using 110V by connecting an inverter to the starter battery. It is crucial to select an inverter that doesn't draw too much from the alternator. It is also good practice to tie it to a busbar in the vehicle that is only powered when the engine is running. A warning based on personal experience: AC charging on EcoFlow power stations is pass through, this makes them ill-suited for this charging method. It is very easy to trigger an error code, and could lead to damaging the power station and/or prematurely age the starter battery.
Both power stations and standalone battery banks can be charged using a DC DC charger. Here too it is critical to stay below the limits of the alternator as specified by the vehicle manufacturer. Here too, tie it to a busbar in the vehicle that is only powered when the engine is running.
One last option: a cheap but basic power station. Dr Prepare makes a 100 Ah LiFEO4 battery with a 12V module that makes it capable of powering devices directly. It doesn't have an inverter, so it won't power a microwave, but for $400, it could be used as a starting point for a simplified DIY electrical system.
https://www.amazon.com/dp/B083ZDL1S...KAX396WM&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it
