This will invaribly be different for each rate and scenario but just a general gauge.Even though rates are in the 3's and 4's the monthly payment or what we call the "mortgage constant," on our end is higher because your payment does not consist of just interest, but interest and and 1/360th of principal on a 30 year fixed loan which is designed to amortize/payoff to $0.00 balance by year 30 or 360 months.Typically a rate around 4's will have a monthly mortgage constant of around .50% monthly (6.00% annual) or about $500 per month for every 100,000.Sometimes when the rate gets into the high 3.50% range the MC is around .45% per month ($45 per month for every 10,000 borrowed) so it doesnt vary much while at 4.50% 30 year fixed the MC monthly is around .507% or $50.70 per month for every 10,000 borrowed.I suppose all this technical speak means is that if you borrow money where the outflow out of your pocket is around 6% with interest and principal considered then you'll probably want to reinvest it somewhere else where you can get considerably higher rate of return on this cash than 6.00% atleast this is how I look at it.If you want to make 6% + 6% for cost of funds then you'll want an investment with a hurdle rate of 12.00% or higher cash on cash as an example.

.  ($100/day, and $50 for a half day.)  

Hi @Cameron YorkI would highly recommend that you just focus on a few states and learn their processes before trying to learn all 50.  

I am familiar with the 1% rent rule which would imply that I should be looking to get around 3500-4500/ month for a house in this price range.  

They are a tad slow but you can often find 50% off coupons and free shipping if you look

It may be 50% or higher.  

There are many ways to pay PMI:- LPMI - lender paid MI which is a fancy term for taking a bit higher rate to absorb the cost of monthly MI for the life of the mortgage, depending on your credit score it may take .125%- .50% more in rate to absorb your entire premium for the life of your loan- BPMI single premium- similar to the above it eliminates the monthly MI premium for the life of the loan but BP part of BPMI stands for "borrower paid," so as you might have guessed the borrower pays this premium in a cash sum at closing either from their own funds or seller concessions they've negotiated from a seller or a gift from their giftors -BPMI monthly or split premium - MI can also be paid as monthly MI which is the stereotypical way to pay MI and it can also be paid as a split premium or hybrid whereby the borrower pays a good chunk upfront to have a greatly reduced monthly MI payment.Most people take LPMI and absorb it through the rate via LPMI to eliminate MI for the life of the loan. 

This is why I have told people inquiring in the past 25,000 up front non-refundable and then 50/50 split.

Do I go with the 2% rule on rents I hear all over BP or the 0.8% rule on rents from The Millionaire Real Estate Investor by Gary Keller?  

When acquiring these old gems, or objective is to improve their energy efficiency by a minimum of 50% (40% on newer, post War houses) while updating the building to provide modern, healthy living spaces for our tenants.