Hi George, welcome (to both of you).
I'm afraid the payload question is a bit " how long is a piece of string!" One person's "adequate" is another's "plenty," and yet another's "can't possibly manage with THAT!" My best advice would be to go for the highest payload you can, (which means only have extras fitted which you know you'll need), and watch what you put in.
There's no maximum length, as long as the max weight is 3500 or less your car licence is fine - but of course, the bigger the van the more it weighs by itself, AND the more tempting to overload!
I'm afraid the payload question is a bit " how long is a piece of string!" One person's "adequate" is another's "plenty," and yet another's "can't possibly manage with THAT!" My best advice would be to go for the highest payload you can, (which means only have extras fitted which you know you'll need), and watch what you put in.
There's no maximum length, as long as the max weight is 3500 or less your car licence is fine - but of course, the bigger the van the more it weighs by itself, AND the more tempting to overload!