You can roll a qualified ESOP to an IRA- I would look at that.
I like your plan and I think you are more or less good to go; I am 47 with three young kids 9,8,6 and I have budgeted a lot of money separately for them for college, weddings, cars and I am going to also give them the option to go to a state school and then I'll pay for grad school. I have almost $1.4mm set aside for them, which is actually probably a little more than necessary, but not much! I guess max funding 529 in Minnesota is $350k?
Also, I think your 3.5% withdrawal rate will work as long as you keep at least 75% in equities and you are comfortable with short term volatility.
I live in CT so my spend rate right now is a little higher, about $240k, but I have thought about relocating to a lower cost area and I think $175k is a nice lifestyle with the house cars etc paid off. Also, I like your farm idea, be interested to see what you had in mind as I could see myself living on a farm- lots of lakes Minnesota. I like NC because we are all swimmers and great state schools!