Really depends on what needs redesigning. You are basically talking about three interlinked projects. As far as possible it is best to chunk down into lots of

Really depends on what needs redesigning. You are basically talking about three interlinked projects. As far as possible it is best to chunk down into lots of small tasks, keeping them as separate as possible. That's one of the huge benefits of webapp world, you can maintain clean separation between functions. I'll assume that you can't just build a complete new site, migrate the data and axe the old one. If the database needs redesign, then you'll need a way to have transactions from the current database propagate through to the new one. You don't want to break anything from the users' perspective while the redesign takes place. If business rules need to be improved, then you'll have to make a decision whether to hit the current database or the new one. Finally, the skin/usability part, keep it modular so that you can incrementally 'improve' your site. You would call the business rule codebase from either the old or new part as appropriate. Just look at Amazon, eBay, Google, etc. They do continuous improvement without breaking much at any given time. The key is to keep each change small, test and be able to revert if something goes wrong. The reversion needs to be designed into every database change to minimise pain and lost transactions. Of course, good project management is key, yes! even with just the two of you working on it. "Failing to plan is planning to fail." :-)