Hi,
I can set the meeting point easier now. We'll meet in Limehouse basin shown here:


When you exit the train station at either exit, turn left


It was 20 minutes on the DLR from Limehouse to Lewisham on my return trip today. Getting from Aldwych to Limehouse by bus took 40 minutes, so I'd recommend the DLR from Lewisham to get to the starting point.
At the end of the walk, at Victoria park, there is a cafe in the park and a number of pubs with outdoor gardens at the north end of the park. You can then take a 20 minute bus ride to Stratford, a 30-40 minute bus ride to London Bridge or a 25 minute bus ride to Canary Wharf.
Nearest undergound is Mile End.