The model to go for is the Sovereign, the cheaper classic has too high a gear range dispite a 20T rear cog. I've tried fitting a 22T but fouls the full chainguard.
Weight wise you are looking at approx 48lbs, although you really only notice that uphill, once going they motor along nicely, if speed isn't the issue then it really won't matter.
The rear carrier is made by Pletscher, you can fit a child carrier in seconds to it without tools, Pashley can supply these for you. As well baskets, bags tec.
If you need anymore info just mail me as I'm a main dealer for Pashley.