I'd be a bit wary of anyone who suggests 24/28 spokes is ok for 91kg, plus extra loading, on urban roads. Just my opinion.
This caught my eye and i would agree with it; I'd want more spokes than that for a heavily laden, urban wheel. Save the low-spoke jobs for a Sunday bike.
FWIW, my GF has Fulcrum 5s on her "best" bike and they've been bomb-proof although she's a little lighter than you Vickster and her bike doesn't have a rack.
For a tough wheel, I'd be looking at 32/36 or, at a pinch, 28/32. More spokes on the rear makes sense since the rear wheel carries more weight, especially when the rack is loaded. As a bonus, more spokes could mean riding home rather than getting a taxi/train/lift if a spoke does break. You've more chance of true-ing the wheel to keep the bike ride-able.
Paul Hewitt (mentioned up-thread) has built several of my wheels and they've been great albeit he's some way from Sutton.
I can't really advise on hubs and rims since all my bikes have disc brakes and most of the rims are disc specific (ie no braking track). I do, however, have a pair of wheels with Mavic CXP33 rims and they look pretty good and Paul recommended them because the deep(ish) rim section also makes them very strong.
I reckon the most important contributor to strength is the build quality followed, probably, by number and type of spokes.
Another advantage of hand-built wheels is that you can probably re-use the hubs when the rims are worn out.