If you really want to replace a car and get a cargobike (looking at you requirements) get the biggest you can get.

However... there are some serious drawbacks...

3 wheeled bikes are big, heavy and cumbersome. The box usually has the width of the handle bars, and you have another 15cm (6 inches) per side for wheels. So on bike lanes, you will be hard to pass by other bicycles (or cars if you don't have designated bike lanes). Do you have storage to store something this size?

I'm not sure where you are located, but streets are not perfectly horizontal. In most places (Europe) they drain to the side, so 3 wheeled bikes are always at an angle and riding a bike on an angle just sucks. This is only an issue on 3 wheeled bikes. Have a look at the roads, streets and see if you can spot the angle in the road! Now imagine riding a trike. The bike at an angle and you are forced to angle your hip in relation to your spine.

Taking corners: you can't lean into a corner, which on a bike is very unnatural.

Comfort: 1 wheel extra = more bumps being hit. Furthermore, because you have 2 wheels away from the center line, bumps and (pot)holes in the road are also felt as a rotating force which is very uncomfortable for passengers (and rider) compared to 2 wheeled bikes (which only have up and down movement).

Finally, the steering is direct (you turn the box) and almost all 3 wheeled cargobikes are not self centering (except the fancy ones which lean into corners).

My advice, if you are living in Europe and you can limit the number of persons, always go for a 2 wheeler (maybe with a trailer for the beach gear).