Are you sure the landlord collected May rent or maybe used one months free rent as an enticement to rent the property?

Start with BiggerPockets Ultimate Beginners Guide (free).

Then, once I have that information/proposal/etc. prepared, how should I approach investors?

They want instant gratification.It's a cold world though, you ain't getting that without a cost.

Excel can easily do all this.You can likely download a free template that already has all the formulas you need.

My thoughts from the little I know about the raw numbers however:1) You have no reason to not raise the rent at least a small amount to compensate for the extra cost of ownership the past few years.

My recommendation would be to own residential first so you have a much better understanding of the costs to own real estate.

Costs the same to put on a new roof. 

It sounds like you'll have well over $100K into it, between down payment and closing costs - is that accurate?

Feel free to reach out if you have any questions!