After you retire, you'll probably need more than $75k/year. While there are some ways to access 401k's after age 55, and tIRA's before 59.5, You probably don't want to do that.
Your taxable brokerage account (I assume the brokerage account is taxable) is the ideal way to bridge your income gap until all the other income sources start up. Spending from taxable allows you to keep your money in your tax deferred accounts, especially the Roths, for as long as possible. This is something that should be planned for, to ensure you have enough to make it past at least age 59.5.
Having said that, you do want to get the money out of the tax-deferred accounts at the lowest tax rate(s) you are allowed. Generally this means leveling the withdrawal amounts + income taken each year, including years when you are forced to take RMD's. You can keep those withdrawals in your retirement accounts by doing them as a Roth conversion. That has the added benefit of adding a bit of your taxable account to the Roth account, when you pay the conversion taxes from your taxable account.
Here's the way I look at Roth conversions:
Withdraw $1000 from a tIRA, pay 20% of it in taxes so now you have $800. Add $200 from your taxable account and put the $800 + $200 = $1000 into a Roth account. That's a Roth conversion, though normally it's a simple $1000 transfer and taxes are paid later from a taxable account.
Mathematically, if you always have to pay 20% in taxes, $1000 in a tIRA is the same as $800 in a Roth account. Both net you $800 after-tax dollars. But you were also able to add $200 from your taxable account and put it into the Roth, where it now grows tax-free until you have to withdraw it.
While you may not be able to contribute more to your tax-favored accounts now, by spending only from your taxable accounts and performing Roth conversions, to the extent that they are beneficial to you, you will delay any retirement withdrawals as long as possible and move some of your taxable account money into a Roth.
