The short answer is that you will get credit for everything that has a written and transferable contract associated with it.Not all side income will be counted towards forcing your appreciation.

Then, my inlaws have agreed to take out an equity line of credit on their house and are going to have a little more than 40k in money that they are going to allow me to use.

Back when my main gig was construction, I did a lot of Tenant Improvement (TI) work in structures like these. 

I suggest you make sure they are qualified (income, background, etc.) and set them up with a credit repair agency so they can purchase the home before the option expires.

There are factors that play into those percentages such as what state project is located in, your credit score, funds you have available, experience, etc...

Even if you are able to buy a house with "no money down", if you have a problem and no way to fix it, you're headed to foreclosure and another 7 years until your credit score is back up so you can obtain financing again. 

Less labor for the deleader ( = less cost to you) and if it's occupied, you need to cover the cost of housing your tenants while the work goes on.There are tax credits for deleading and loan programs in MA that you can use that don't have to be paid back until you sell the unit.

Go to a credit union and inquire about a "porftolio loan" typically 20% down, 20 year amortization with a 5 year rate adjustment.

Bill tenant for overage but no credit for underuse.

@Daniel Johnson Try to setup credit with suppliers, most will once they see your monthly transaction.