1. Transferring your funds from a traditional IRA to a Roth IRA is a conversion, not a rollover. There's no limit on the number of conversions you can do each year, so your method would be fine. However, you don't need to do the conversions separately. You can make your nondeductible contributions for each year, and then convert the total at once.
2. You can use the same traditional account for your 2024 and 2025 contributions as well as future contributions.
