I'd like to sense-check the following scenario, to make sure I don't do something phenomenally stupid and irreversible. I'm hoping that I've correctly understood what I've read on this site & elsewhere. I am only asking about US taxation (ignore UK taxes for now).
I am a dual US+UK citizen living in the UK. I have $340k in my 401k (all contributed while working in the UK for an American company). I will roll over my 401k into a traditional IRA (no tax implications here). I do not have any other US-sourced income.
I currently have $77k in general limitation foreign tax credits carried forward.
I plan to expatriate on 8 January, and will arrange to have zero UK or US income during the first week of January.
HOPING TO CONFIRM / SENSE-CHECK
If I do a $300k Roth conversion on 5 January (just before expatriating), my entire US taxable income for the year will be $300k. The US tax on this is amount is $74k. This can all be classified as foreign-source income, and so the $77k I have in tax credits should entirely cancel out this US tax liability?
The following year, I convert the remaining $40k to Roth. Now as a nonresdient alien, I no longer have tax credits or a personal deduction, but my US tax liability (Form 1040NR) for this amount is ~$4,807. I think this is more tax-efficient than converting the full $340k all at once?
Do I even need to wait until the next year, or can I Roth convert $300k as a US person in January, $40k as a non-resident alien in February, and these two transactions will still be considered entirely separate?
Thanks for any confirmations/corrections/critiques of the above game plan!