A few thoughts
- To control the Multiplus you will need to choose either 1) a Victron VE.Bus Dongle which lets your phone control it, 2) a Victron Digital Multi Controller (panel that is wired to the inverter) or 3) A Cerbo GX computer with touch screen that is more expensive and overkill for some.
- To program the multiplus for your specific batteries, some dealers will do it if you know what batteries you are using. Otherwise get an MK3-USB adapter that lets you do it with a laptop.
- Assuming you are using lithium (LiFePO4 or LFP) batteries, a Victron Smart Shunt is nice to have to give you an accurate reading of state-of-charge. Some batteries will show this on an app but they are notorious for getting inaccurate if you don't charge up to 100% regularly.
- To charge from the bus alternator, the best way is a DC-to-DC charger (LFP). The Victron Orion XS is a very capable unit that is programmable up to 50A
- If LFP batteries, your main fuse should have a high "AIC" rating - good choices are MRBF and class-T fuses. They are somewhat expensive but you only need 1 as the main fuse and the downstream fuses can be cheaper.
- If you want solar you would also need a solar charge controller, but sounds like that is not in the current plan.
Lots of other smaller stuff to be careful with but that is most of the medium size stuff.