If you have a 2 bedroom house, that's 2 bedrooms whether the house is big or small. It would have to be a rather unique situation for you to add another bedroom. If you're thinking about finishing a room in a basement, say goodbye to your $15k hypothetical equity. Keep in mind that you have to make sure that you're offering your potential buyers (the investor) a good deal.
So let's work backwards. You're talking about marketing this property to other investors as a possible rental. Suppose retail indeed is $125k and rent is $900 for this 2/1. Buying retail is a far cry off our 1% rule. 1% rule suggests that the investor should be looking to acquire this place at no more than 100x the rental income, or $90,000. Maybe the house needs some moderate repairs, let's say $5k to get it rent ready. Discount that from the price, now an Investor wants it at $85,000. Of course, you're looking to take a cut while wholesaling, let's say $4,000 for fun, you would need to have a contract for $81,000. Make sure that you're offering your potential buyers (the investor) a good deal.
Step one is securing accurate numbers. Rent, ARV (After rehab value), cost of repairs. Then you can calculate the amount you want to offer in contract. While working on the contract negotiations, you should be simultaneously searching for potential buyers.
Suppose your accurate numbers say you'd need to have a contract for $70,000. Yikes, doesn't that seem pretty low? Well, it depends on the needs of the seller. Does he need to pay off an outstanding $100k mortgage? Then walk away, it doesn't suit your criteria. ...But Maybe ask about his other properties before you leave. Does he primarily want to liquidate this free/clear property? Offer him a quick close at $50,000 (leaving room for negotiations). Does he have 4 similar properties, and doesn't want the headache of listing all of them? Offer contracts on each of them, getting him a much more substantial sum without all the hassle.
Your profile says you're a student, and your family doesn't own any homes yet. Where are you living now? Finances aside, could you move into this place and rent out the other room? If you're renting, it makes as much sense for you to stop paying someone else's mortgage and start building your own equity post haste.
Maybe, while finding out this guy's needs, you discover that he's not necessarily trying to liquidate immediately. Maybe he owns it free and clear, and is waiting for the right deal to come along. Would he be willing to Owner Finance the property with a balloon payment in 3 years? By then, you'd be 2 years out of college with verifiable income in order to qualify for your own mortgage through a bank, and buy him out of the property.
couple other notes:
-If you're wholesaling, you don't need people to help finance the deal.
-asbestos, like lead-based paint, is not a concern unless you disturb it during renovation. Although it might be a concern for the person you're wholesaling to.
-If you're calling their realtor, chances are good that this is already not the opportunity for you. Realtor is likely to push for max dollar from conventional (bank) financed buyer or may seek out passive investors who have 25% down for a turnkey property.
I mostly typed this wall of text because I'm relatively new as well, and the brainstorming feels good to me. Hopefully this will help spark some others' thoughts. Regardless, I recommend not letting the excitement of a deal overwhelm the rationality necessary to close a profitable deal. Your priority is not acquiring this property, your priority is acquiring any profitable property. If it's not profitable, simply walk away.