IMHO most obvious hole in your process is missing bug tracker.
Get one free, like TRAC. It includes wiki for technical documentation.
Every feature should start as a bug in bug tracker. Get developers write whatever thoughts they wave to bug and/or wiki pages linked, so few months later you will be able to recall what assumptions developers made when coding.
Bug tracker will force some process/workflow. Then you can start thinking and talking how you need to tweak it to fit needs of your group, and what other tools you need to involve.