"The venue, together with most hotels and most of the major tourist attractions, is in Zone 1. This zone is the cheapest to travel within." - Zone 1 is the *most expensive*. Try to stick in a single zone and not cross zone boundaries if you can.
"Beware: London buses do not take cash! You will need an Oyster Card, which also covers cheaper underground travel." - they do accept contactless payment cards though 220.127.116.11 15:14, 1 August 2014 (UTC)
Are you familiar with London and/or able to read maps?
I am uploading lots of photographs to Commons:Category:Walking routes for Wikimania 2014 that illustrate the walking routes between the Barbican Centre, Thistle City Barbican, Travelodge London Central City Road, Wikimedia UK offices and Barbican, Moorgate and Old Street tube stations.
These need transforming into illustrated walking guides on this wiki the conference. More photos are being uploaded all the time, so keep checking back if there are ones missing from the routes.