This is it, why you have a motorhome, somewhere to stay. It might have to serve several other roles as well but without this one then it isn't a motorhome.
In the UK there are rules for the authorities accepting a vehicle as a motorhome or motor caravan and while they can be dismissed as just rules, they generally make sense as to what you will want.
Odd requirement to state perhaps but it means that there will be a door to go in and out by with the priority given over to the accommodation space. Using the driver or passenger door doesn't count, but you can use the accommodation door to enter the driver and passenger seats.
For convenience this wins. Not always pushing past seats, you can get in and out without asking people to move etc. There could be a safety issue, such as getting out in an emergency, but from a practical point of view, having a door dedicated to living in the van is a good option.
Campervans without beds are called day vans. Nothing wrong with that and if that works then great. If you want somewhere to sleep then perhaps you have an awning or a separate tent. If you want to just pull up and put your head down for a good nights rest then a purpose built bed is ideal.
The immediate option is to build a bed in the van. This can use a lot of space up, but when it's done its always there, ready to use. To save space, permanent beds are often raised up to the top third of the van height and the space underneath used for storage (sometimes called a garage) or perhaps cramped living space. These can often incorporate bunks etc. We did see a large van with sleeping for eight in four bunks either side of the van rear and carrying nine people.
The other common option is to convert existing furniture into a bed, nearly always the seating, where support is positioned and the cushions are rearranged to form a mattress.
In some instances the floor is used, and even kitchen work surfaces adapted.
A third option is the fold out or drop down bed, where the bed is stored ready made, either held against the side of the van to fold down or lowered from the ceiling on pulleys or rails.
Yet another option is the hammock style, where the bed is slung from hooks, either as a traditional hammock or as a ridged structure.
There are lots of options, but all a trade off between space and convenience.
The biggest thing to consider, is that you have to sleep in it so if it's not comfortable, you don't have space, it's to hot or cold, then its not going to be a good bed and you won't be getting the best rest you need.
Everyone needs water and accommodating it conveniently in a van is nice to have. Realistically this could just be a plastic or metal can with a pourer, but small water systems are nearly always created with either a permanent or removable tank, pipes and taps, and a waste system.
The basic is would be buying bottled water from the shops and using that. There are a surprising number of people who do just this.