Also, I see the total purchase cost add $3,700 instead of subtracting that amount.

I just wrote this article a couple weeks ago...maybe it gives you some things to consider along the way-https://www.biggerpockets.com/renewsblog/considera...More specifically on the numbers, calculate what you'd be profiting (don't forget to subtract mortgage interest and property taxes and all that) and compare that to what you would pay in rent. 

I want to try and keep my costs under that amount.  70% gives me a little buffer encase my Rehab goes over budget or the appraisal comes in lower than expected.Then it’s just a matter of subtracting all my costs to figure out what my max offer can be.  

Instead, the full amount of the property tax is calculated at the applicable rate, then the amount of that tax attributed to the school tax is subtracted from the final property tax bill for owner occupants. 

Either repair before settlement or subtract from the cost of the house.

What we most often see is the rent is about the same as for a single family home investment, but then subtract $200-$300/a month HOA fees or more and your returns go down 20-30%. 

If it is cash flow you will need to determine how much cashflow you want to make each month from the property, then work backwards.if you want to cashflow $1,500 per month from the 6 units you will need to add up the monthly revenue (rents) then subtract all your monthly expenses. 

Do you subtract expected capex?

Subtract that and all other expenses from the rental income and you will likely have negative cash flow on the property itself.

So always look ahead and make sure that you add or subtract months on the lease to make sure it ends at a great time for you!