@Chris Swindell I applaud you for wanting to help your mom and trying to make this happen. If you were buying this house to live in yourself, I might say it's a good deal, but as an investment I don't think you can make the numbers work. Upfront I agree with @Paul Choate and think you're better off just selling it outright and being done with it, even if you get less money.
You mentioned your mother would have a hard time selling this through traditional channels. Why is that? If you don't think the property would sell for $40,000 going through the traditional route, then you definitely shouldn't pay $40,000 for it off market, no matter how good the terms are.
But let's take the current offer you have and look at your options. You buy the house from your mother at its supposed market value of $40,000 with $0 down and 5% interest amortized over 10 years. Your monthly payment is $425. Since you're not planning to live in the house, you can either rent it out, sell it on a wrap, or sell it on a lease option. I'm going to rule out lease option as they often don't work and are a pain, and can be legally tricky sometimes.
If you rent it out for $675, you have to budget for expenses in addition to your PITI. I would budget 10-15% of rent for repairs and capital expenditures, another 10% for management, and another 8-10% for vacancy. These are all necessary. And since you don't live in the area, it's going to be a pain to manage all of this from afar, even if you can find a good property manager (which is a big if). Or you could use the lease to make the tenants do their own repairs, but that can be hit or miss. So let's say you budget 30% of rent for all of this, which comes to about $200 a month. Add that to your $425 principal and interest payment, plus the $75 you budgeted for taxes and insurance, and now your cashflow is negative $25 per month. There's simply no way to make this cashflow as a rental property with a 10 year, $40,000 fully amortized note at 5%. If you had a 30 year mortgage, or at least a 30 year amortization with a balloon, it might work, but I still think it's too tight. And without a downpayment and buying it at full price, you have no equity cushion in case something goes wrong. You could easily end up selling the house at a loss in 5-10 years, as Paul mentioned. If you could buy the house for $30,000, or buy it for $35,000 and put $5,000 down, it could potentially cashflow. You can run different scenarios all day, but the only way to make it work is to either buy the house for less money or extend the note over a longer period of time.
Or, you can sell the house on a wrap, which you proposed as your plan. Wraparound mortgages are perfectly legal in most states, although not without risk. But in this case, since you're buying from your mom and you can include in that contract and deed explicit permission for a wrap, it's not a big deal.
However, anyone who's going to buy a $40,000 house isn't going to be able to afford $700 per month, and if they can afford it, they can likely go to a bank and get a traditional loan. I'm not sure where you got that number from. Let's say you are able to find a buyer who can't get bank financing and is willing to pay a higher interest rate to buy off market and have a junior lien (and if you're unfamiliar with the area or how this works, you may have a hard time finding those people, especially without a realtor). You sell the house to them for $42,000 with $2,000 down as you said. You then finance them $40,000 at 9% interest for 10 years. That puts their monthly payment at about $500, and they're paying for your taxes and insurance, so you're barely eking out a little cashflow over your $425 monthly payment. But most buyers want a 30 year note, or at least a 15 year note. In order to get $700 per month on a 10 year note like you proposed, you'd have to charge around 17% interest, which is essentially illegal (I won't go into usury laws or possible Dodd-Frank stuff here). Around 9-10% on seller finance is standard, so consider that your high end. But I would also want at least a 10% down payment, since if they stop paying and you have to foreclose, you could easily spend more than that in lost rent and legal fees, plus any damages to the house. Keep in mind a larger down payment also means a reduced note amount and reduced cash flow. You would also still have almost no equity in the house.
Anyway, I could keep playing with numbers, but you get the point. If you lived near the house and could help manage it, it might be different, but I think the numbers are tight any way you look at it, unless your mom is willing to sell it at a cheaper price. Keep in mind she may get the same money selling to you at a cheaper price rather than going through a realtor. I'd probably just sell it and get rid of it. Whatever you do, make sure you use a good attorney in Oklahoma who specializes in real estate and understands investor transactions.
Or, and I'm tried of typing now so I won't go into great detail, you could possibly do a Joint Venture with your mom where she (with you as a partner) sells the house to someone else on owner financing, gets a down payment, and then finances the rest at around 9% for 15 years, but you agree that you will find the buyer and manage the payment collections, dealing with the buyer, possible foreclosure, etc., in return for X% of the cashflow. Still some risks and legal complications. Just a thought.
Good luck!
Chad
(Disclaimer: None of this is meant as legal, professional, or financial advice.)