You are getting mis-led by the taxable nature of each account you have. Don’t think of those account boundaries as hard boundaries (Roth, IRA, 401(k), HSA, taxable bank, taxable brokerage). It’s all just your stuff, and money is the most fungible thing around. Tax rules are dotted lines.
Who told you you couldn’t keep your cash emergency fund in your IRAs? It can be in taxable or IRA.
Now, having said that, I would always keep some cash in taxable accounts, just because if you have to make an emergency car or roof replacement or have an emergency bill late in the year after you’ve already done your Roth conversions and other taxable IRA distrubtions, you don’t want that emergency IRA pull to pop you into another tax bracket or toss you off of another IRMAA cliff. As to that amount I can’t tell you how big it should be, it just depends on your risk exposure.
How I plan to do it… I set my taxable cash limit at (shall go no lower than) $200k, not including any planned special projects (I’m going to set aside more for house renovation and a new car).
But I will spend down my taxable cash to those limits, and then I will do a combination of taxable IRA distribution and Roth conversion such that I can feed myself and also do some Roth conversion.
In practice, I will feed myself from IRA from January-November, and then around December 1 of any given year decide how much room I have left for conversions to fill up whatever tax bracket I want and/or stay away from whatever IRMAA cliff I want.
But I think your advisor could be correct, if you’re quite affluent with tax-deferred assets in the millions, and nice pensions, then you have to shed that tax deferred money. Somehow. Especially before one of you pre-deceases the other, the survivor will get absolutely shafted by tax.