jds - Very good question. We didn't actually consider much the comfort of back seat passengers. Here in Africa, we usually travel two men in a vehicle, with two to three vehicles in a convoy (generally an FJC, a 70 Series, and a Defender, or the FJC with two 70 Series, or the FJC with Hiluxes or Prados from our offices). The ONLY scenario where we envisioned ever having people in the back seat was an emergency or a situation where another vehicle was immobile and the two men in that vehicle would need a ride back or to the next RV point. In total, I can count on my two hands the number of times I have had more than two people in my FJC (and that's over the course of two years).
As we saw it, there were two main benefits of the Access Cab, and neither had to do with additional passengers. First, the seating position in the Access Cab is far superior to the Single Cab, as the Single Cab's design forces a rather parochial seating position for the driver that isn't ideal for long drives. Second, the Access Cab allows for more things to be stored securely in the cab. We figured we could safely store: two TNF Base Camp XL bags or four TNF Base Camp M bags or two 1520 Pelican cases and one TNF Base Camp XL bag. Since we're usually moving with a combination of these TNF bags, TNF tents, and Pelican cases, the distribution of these items between secure and non-secure (bed) areas in each vehicle is important, particularly if moving with other open-bed (79 pickup, Hilux, etc.) vehicles where secure interior space is at a premium.
As for the bed, your estimate is good. We ended up taking a 73.5" bed and making it into a ~62" bed, but adding a lot of utility in the process in tie-downs, a universal rail system, space for two-deep Rotopax, permanent Hi-Lift mount, etc.
Some more have emailed with the "how do I do this" career questions. The truth is, a lot of it is luck. I studied law (undergraduate) in the Netherlands and then in the U.S. (J.D.), then ended up going to business school and earning an M.B.A. with a concentration in Economics at the University of Chicago (where I try to stay quite involved, serve on the Admissions Committee, am an Executive-in-Residence, etc.), and finally ended up working as a full-time economist after deciding to do an M.Phil. and Ph.D. at the London School of Economics (one of the best decisions of my life, and a fantastic place to be a postgraduate student and researcher). There's no shortage of work for economists with a strong business/consulting/banking background, particularly those of us with international experience/expertise. But choosing the right work is sometimes a gamble, and I've always been a believer in the Tarzan school of career planning - try not to let go of the last vine until you've got a firm hold on the next one.