@Robert Kirkley, when I was your age, I would play this game to further squeeze my expenses down: when ordering fast food, I’d find what I want on the menu, subtract a dollar from that total, then use that amount to order something else.

I've always been interested in Finance (especially in Hedge Funds) starting at the age of 15/16 years.

welcome to the wonderful world of making money in Baltimore real estate, I am 77 years old and started investing in houses when I got out of the Army in 1962 at age 20, well I should say that I started taking real estate courses, most of them were rip offs, but I learned some valuable lessons, like "Don't put a label on yourself, like "Wholesaler, flipper" etc. just be yourself.

Both from age and elements and also tenants who tear things up.

New Roofroof age = 20 years or 240 months (guessingCost of new roof $7,000 (guessing)$7,000 / 240 = $30 per month (I added this in repairs)New Furnace (i do not know if this is 2 or 1 furnace)Furnace Age = 20 years or 240 monthsCost of new Furnace $2,500 (guessing)$2,500 / 240 = $10 per month (I added this in repairs)2 new Water Heaters (1 for each unit)Water Heater Age = 12 Years or 144 monthscost of new Water Heater $1,000 Each$1,000 / 144 = $7 per month for each water heatersWhat you guys think?

I wouldn't rely on the 50% rule as the expense ratio can vary - I've seen anywhere from 30% - 60%+ all depends on the product type, class, age/quality/condition, market, who pays utilities, etc.Generally speaking for B/C product built in the 60'-70's and 70+ units I've seen expenses range from $3,700-4,500/unit per year.

Find similar properties (what we call comps or comparables) based on square footage, lot size, bedrooms, bathrooms, age, etc. and use those as your ARV.Networking within a group is great, but ultimately the numbers you're analyzing will come from experience and will be situational (every deal is different). 

Use part of what you have for a down payment to the owner ( keep some in reserves for unexpected issues) see if he will carry the remainder of the loan for at least 5 years or possibly the life of the loan depending on his age and what he is needing/ wanting out of the deal.

I replaced three roofs on my properties over the 10 years at significant cost.(2) Do not discount the age of the housing stock. 

Found a place where the numbers were there but just too many problems between sketchy neighbors and the age of the house to pull the trigger.