walker said:David, Now I don't know how to believe you as you said mountain and Essex in the same post and we all now Essex is flatter than american roadkill.
Someone might tell you different but I would start with the 10-15 miles a day and slowly build that up to your required distance.
I've never ridden a bent so can't really go much further than this so I hope this helps
Walker, I'll meet you at the Tilbury-Gravesend ferry and take you on a trip of the Essex hills! No seriously it's not known for it's up and down, but the trip South to North from many points along the estuary hits hills eventually. For example my trip home tonight which I'm doing on an individual time trial basis wind permitting will be flat(ish) for 16 miles from the City up to a line parallel with the Dartford crossing and then a further 16-17 miles east which will have some hills on it. You can actually go round them if you vary your route but it's worth mixing it up for the variety.
David, I would mix it up as much as possible as BTFB said. However I would keep the trips short(ish) initially as your body needs to adapt. When I came back to cycling six-seven years ago I was doing 10 miles a day max, five miles out, five miles back. When I was up to it and feeling strong I would try and beat my best time and really push myself. Towards the end of the week and when I felt tired I would slow down and listen to my body. The weight still come off. Over a period of six months continuous cycling I lost about two stones (and I've subsequently put on a stone, but that's another matter) and I ate pretty much what I liked.