1) Your first five years' income should probably come out of taxable accounts first, and then Roths if taxable is used up. Reasons: Can't do early withdraws from traditional IRA or 401k without a penalty at your age. Roth ladder will be funded from trad. IRA or 401k.
To execute the glidepath towards a higher equity allocation, you want your taxable account to be mostly bonds so that the desired adjustment occurs as you cover living expenses. Usually, allocating dividend and interest generating assets to a taxable account is a bad idea, but with yields as low as they are I don't see the point.
Remember that the purpose of your low-yielding bonds is to provide an alternative to selling stock in the event of a correction or recession. So, in the event of a slump, you would want to apply this function and live off of proceeds from bonds until things recovered. Your AA might change when you do this, but what else would be the purpose of the insurance? Others might argue for a consistent, preplanned AA in this situation no matter what, so pick a side and make it your plan.
In general, I'd create a basic spreadsheet plan with all your accounts, their current values, and your target allocations. For each year, show from where the living expenses are withdrawn and model the effect on AA. Try a few different strategies. Create an annual instruction set for yourself to follow.
2) The biggest mistakes I can think of would be:
(a) Withdrawing from a traditional IRA or 401k and triggering the tax penalty.
(b) Failing to fund the Roth ladder - even for one year!
(c) Your capital gains will be low in those first years because you are selling more bonds, which presumably have not appreciated. Don't get used to low taxes though, because when it comes time to sell more equities, capital gains will be much higher. Think this out when budgeting (past the initial years.
(d) Thinking bonds cannot decline in value. 30 year treasuries do not count as a bond allocation for your purposes - not at these low rates. Keep the durations short - like 3-5y so you don't get burned by rising interest rates.
(e) The usual stuff like becoming a day trader or trying to juice the 4% rule with dividend stocks, junk bonds, market timing, or other forms of risk concentration.
3) You might toy with making those first 5 years super-frugal to increase your odds of long-term success. E.g. downsize housing, hold off on big vacations, go down to 1 car, etc. After a few years, you will either be really well off or you will be aware that you retired right before the Great Crash of 2020, in which case it'll be a good thing you went the frugal path and got used to that lifestyle.
