Under New Management

The 401k money goes to me, then i pay the seller, so it will be in my name with no debt tied to it. I will still have to pay the loan back (it automatically comes out of my paycheck) but it isn't in any way connected to the house. So yes, I will still owe money for five years. Think of it as a personal loan, where they don't care what you spend it on, it's your money, do as you please. But I can go to the bank and get a home equity line of credit for the things the house needs, a couple appliances, some window trim and a few minor repairs. After that I can bank my money and I will be very comfortable financially. The gains for exceed the losses.

1st, congrats on a huge change in your life while IMO landing on your feet on a much more solid and stable ground, up higher.
(For those that do not know or have a 401K...)
That 401K loan has a minor percentage point rate that you pay yourself back on. So it is a win win. While the money is always better off in the 401K, this is a worthy use of the money.
(Debt consolidation is another but not advised)

Real estate is the best area to put your money and since you really need a house and not an apartment, this is a huge win for you since the value of the house will rise and more so with improvements and updates to it.

Staying with your stepson speaks volumes about him as well as your relationship with him.

Enjoy fixing up and straightening out the house.
Best of luck to you. Enjoy!