Backdoor Roth IRA vs mega backdoor Roth 401k

Hi, I did a traditional IRA to Roth IRA backdoor Roth IRA conversion for $6500 in 2023. In 2024, I'm doing a mega backdoor ROTH conversion of my after-tax income to my 401k. Currently, I have two accounts. One is the Roth IRA account that I opened in 2023 with $6500 and Roth rollover/Roth in-plan conversion as a source in my 401k. Do I need to pay taxes for either one? Should I just maintain one Roth IRA account for all these funds? Can I move the funds from my 401k Roth source to the individual Roth IRA account or vice versa? Do I need to pay taxes for both accounts now? What's my best course of action to pay the least amount of taxes?