Would not start the pipeline while still in the 25% bracket.
Since your plan is to retire once you are 55, you can always withdraw from your 401K, or a SEPP won't be as difficult for you as it would someone retiring a decade or two earlier.
Yes on the tIRA provided you don't have intentions to do a backdoor Roth IRA in the future. If you are looking to fund a Roth via the back door, you'll want to leave this in the 401K to avoid gumming up the works.