Retirement tax questions

Thank you for the detailed explanation, this is very helpful and insight. I need to check the fees associated if i keep it as is, but i was targeting to do a full conversion and paying the taxes. I wanted to follow up and ask if i should pay the estimated taxes when i do the conversion say around Oct month or should i pay the taxes when i doing taxes next year. I ask since i am expecting some tax credits due to solar program. Also isnt the 12k in taxes an estimate and the actual taxes will be based on my gross income levels for the year?