(1) Not sure what your plans are with regard to paying for your kids auto insurance when they begin to drive, but assuming you are going to fund it, you can expect your auto insurance costs to go up dramatically. While you could just make your kids pay the cost of insurance, I think that in all likelihood, it will mean they will not be driving (legally anyway) as the costs to insure teens is beyond the ability of most kids to generate that kind of coin.
I have heard up to $2000/yr increased insurance for 1 kid. I expect that expense to fall on us (mostly) for a period of 1-6 years, but I think the expense starts dropping in year 3 or 4 in our jurisdiction. Given our access to transit, this is an expense that could theoretically be cut if we had to (but maybe not the 1st expense). Unfortunately we have 2 kids 1 year apart so it will be double the expense for a few years.
(2) Your home maintenance expenses seem way low to me---a general rule of thumb is 1% of the home's value, and in my own experience, that figure never seems to be sufficient. (Maybe I just bought a money pit.) Obviously, your own experience will vary based upon how handy you are, type of home construction, etc.
My number works out to right around 1% of house value to cover big ticket items, plus the small stuff I spend routinely each year. For total turnkey operations with someone else doing everything, I'd say 2-3% is more appropriate. So far I'm handy enough or savvy enough to contract well for services and not have too much out of pocket. And we'll probably hit a few largish deferred maintenance items before FIRE (or specifically set aside $5k-10k or whatever for these).
(3) Medical/dental also seem very low to me. It sounds like you know the details of Obamacare better than I do, but I would be surprised if your out of pocket costs are as low as you have budgeted. Also , even if they are, given the economics of medical care (costs seemingly ever increasing), the current US Budget situation (not swell), as well as the reality that over the next 60 years, the Dems are likely to lose the Presidency at some point, I would not expect what you will currently be able to get for free to continue. I think it unrealistic to expect that current promises under Obamacare will be able to be maintained in the long run. In short, I think you need to plan for higher out of pocket medical costs. Hopefully, I am completely wrong.
I may tighten up this area of budget some more. Maybe what I have is inadequate. I still don't have a good feel for what we'll owe under an obamacare exchange subsidized insurance plan. My understanding was max out of pocket is somehow limited based on AGI (and ours will be low).
My crystal ball says obamacare gets repealed either very soon after 2014 (within a few years) or not at all. Tinkering may happen but killing it seems unlikely once it is engrained in our society and thought of as an entitlement. Maybe it'll take more than 3 years, who knows. I can always go back to work if access to health insurance is a concern.
But, yes, this is a risk.
(4) Given your nest egg, seems to me that you may want to consider LTC insurance, or at least recognizing that some of your assets may be needed to fund those expenses towards (hopefully) the end of your life. Obviously, shXt happens, and you could need that care tomorrow if you end up walking off a cliff on one of the hikes you take with all of your new time off. Again, an accident like that would have a pretty immediate impact on your assets (drawing them down). In the same vain, you mentioned several times about possibly needing or choosing to go back to work later--if you feel that the possibility exists, seems to me you still may need life insurance. Your current assets may not be sufficient to fund future needs, and if you are gone, you may want to leave those resources behind for your family. Finally, given that you own a home and have pretty significant assets, you may want to budget for an umbrella liability policy. (No, I am not an insurance salesman--just someone who is afraid to leave his house.)
Financial shortfalls that necessitate going back to work are likely to be triggered by long term poor stock market returns. I may coincidentally meet my demise prematurely or (worse?) end up incapacitated to the extent I need LTC early on. However injury or premature death are largely uncorrelated with stock market returns. Hence, the cumulative probability of early death or needing LTC early in life AND having portfolio failures are getting down in the fraction of a percent range.
I (and DW) will accept a 100% probability that we won't have to work right now in exchange for a <1% probability the survivor may have to work at some future point in life due to spousal early death or incapacity AND portfolio failure.
And there is always SS survivor's benefits that protect us for 5 years after quitting work (longer if we have self employment income subject to payroll taxes that earns us creditable SS quarters).
For the typical needs of LTC in one's 60's or 70's, I don't have LTC included in my ER budget. If my portfolio doesn't grow over time I'll be screwed I guess. Of course if money is that tight I would probably choose to go back to work at some point early on.
(5) I believe you indicated you were a Fed Employee. If so, and I know you know this, leaving work now will basically leave you with no federal pension benefits. While a federal pension is not great, it certainly is a meaningful amount of money, and would provide you some additional financial security. By leaving, you do give up a pretty significant benefit.
Not a Fed. I have 2 years service at the current gig, will have 5 years at age 35 when I plan to be FI. That gets me a pension large enough to buy a really nice cheeseburger a couple times a month. Unfortunately it would start 30 years after I retire, at age 65. In other words inconsequential, and I plan to roll my cash balance out of the pension and into my 401k. ~20-25k is all it will be in 3 more years.
(6) I certainly did not have your assets when I was your age, and for you to be able to even consider retiring at 35 is remarkable. I would not be able (or perhaps the right word is willing) to live on what you are proposing to do for the next 50-70 years. But I do have a great deal of admiration for someone who has the courage to do this. I am not as brave as you. Whatever happens--I wish you well.
Thanks! It is a little daunting to think about locking in a budget for many decades. On the flip side, maybe I'll get bored and find something that interests me and has enough of a pecuniary advantage that I'd rather trade my free time for money. Or maybe I'll do the "just one more year thing" for a year or 3.
. Of course, I wouldn't be brave enough to pull the plug this young, but it's very educational for anyone's planning purposes. 
