There are a few things that are mixed here. You aren't spending the Roth money, you are just moving it between accounts. These recharacterized Roth contributions are actually available to you after 5 years. So, staying on your plan, you have the Roth contributions available as a backup.
Next, the 4% rule was formulated for a 30 year retirement. You are trying to apply it not just to a subset of your money, but also a subset of time. Over a time period as short as a decade, there is a higher level of uncertainty: while the Trinity study assigned a success rate of 93% even for a 6% withdrawal rate, you have to be worried about the *next* 10 years, since we have had a great past decade. Here, you are using a strategic tool for a tactical decision; you need to get into more details for a real plan.
There's nothing wrong with this as a base plan. You will have to understand it is planned for "nominal" performance, and you may want to consider alternatives / worst case scenarios to develop your backup plans.