It sounds like a logical move.
My belief is that the 457 works the same as a 401k for this - any sales inside it have no tax effect, the tax effect comes from making "distributions" (withdrawals, aka taking the money out). Learn the rules for sure though.
Consider making a year by year plan for what your expenses and withdrawals would be. Learn the tax and penalty implications of your plan, so that you are calculating the results correctly. Even though your spending and return assumptions might be incorrect, at least you will learn how an example will work. You may learn about cash flow issues you have to solve, as well as the impact of using different accounts at different times.