I am getting some rough outlines loaded here, for each Topic, to give you some of the ideas to start thinking about... I will refine it as time permits.
On size and location of beds, the most common layout is the Island Bed. The reasons that the bed is most often in the front of the van, is to take advantage of the nosecone. By putting the beds up in the nosecone area, you gain more storage space under the bed and you gain about 400 mm or about 16' in floor area in the rest of the van. Now some people find the bed too high when they first see it at the Shows, but you can have a raised floor area to use as a shoe locker, and when you step up on it the bed seems no longer high. This gives you 400mm more floor area in the van, more storage under the bed and cargo hold, and added storage for shoes under the raised floor area on one or both sides of the bed. A win in all aspects...

The Yacht Berth (sideways bed) gives you about 2 more feet of practical layout in a van because it is 1500mm wide as a Queen, where a queen length is 2030. You also gain with two large floor to ceiling lockers, His and Hers, on each side of the bed instead of the wasted space to walk around the foot of the bed.

Now what is wrong with this Yacht Berth layout? Well it is more difficult to make the bed, you have to live with fitted sheets, and the last person out of bed spreads out the Doona. It is a bit of an effort to get up on the step besides the bed, and up on one knee to change the sheets on the bed. The other disadvantage is that the person who gets up most during the night sleeps on the outside, and they need to be a heavy sleeper. The other person has to get up on all fours and dog walk sideways over them to get out of bed. Me? I lived on yachts for 20 years and almost all berths on yachts are this type for safety at sea and I do it for the added floor space equal to about two feet of van. I have always had a yacht berth and still do today in my own Bushtracker. But if you are not fit, overweight, bad knees or hips, or a light sleeper; you may well be advised to avoid this sort of layout.
Single beds have almost the same affect as the yacht berth, with more floor area in the van, as again you do not have the walk around area at the foot of the bed. This they have the ability to have a shorter bed on one side to enhance the layout. Something to think about there.

Overall, we probably do about 60-70% in Island Beds these days, maybe about 20-30% in Yacht Berths, and say 10% in Single Beds. The only other consideration is Resale, but quite often people will take what they can get, as the Second Hand Market is often very tight with respects to Bushtracker Vans. I have seen months with 25 for sale. You would expect to see as many as 50 for sale Australia wide given over a 1000 vans out there. But quite often there are far less for sale, and I have seen months with only two or three or none for sale. My point is, get what you like, so far there has always been a solid second hand market for Bushtracker vans with some people paying more than New Prices not to have to wait for one to be built.
To take and put the beds at the rear of the van, loses the added storage under the bed in the cargo hold, and about 400mm of floor area as the bed is not elevated into the nosecone. And sometimes at the Shows, you see a bed sideways, with a walk around both sides and the foot of the bed. Measure it, it is deceiving. There is not the room to have a descent length of bed, AND walk around the foot of it... Cute trick at the Shows but it does not work...
When I have time, I will try and add layout illustrations to these postings, just samples, for your convenience.. OK?
Kind Regards, stg