[eluser]Aken[/eluser]
First, sit down with whomever you need to and create a plan. This is the most important thing you can do to prevent problems in the future. Figure out
exactly what you're going to do for the next phase: what to add, drop, change, fix, etc. Try your damnedest to never deviate from this list, or things will take longer and longer to get done. If this involves doing different stages of features released at different times, then fine. But have a PLAN.
Second, make sure you have a development environment that is completely separate from the current website, where you can work on the new version of the website. Copy everything as it stands and start from there. Learn about how you can change config values based on environment (the user guide explains this), which will allow you to integrate the new site without having to change a ton of details. Then I'm sure you'll want to continuously update your dev environment with data from the live one, so make sure you allow yourself to do this, either by not changing the DB much, or by creating a script that allows you to import data.
You may need to consider how you will integrate existing data if you do need to change things. For instance, Ion Auth might use a different DB setup than what you're currently running for users and sessions. If that's the case, you'll obviously need to port that data to its correct format, which may involve a SQL or PHP import of some sort.
Third,
test. Maybe create a password-protected subdomain on your production server and try to test as much as possible, to make sure you don't run into bugs that are specific to your production environment. Try to discover as much as possible before releasing the code publicly.
