You should use whatever the standard is for your area and type of property.  

I am approved for the 1 Million dollar credit line, but with only 150k disposable, I won't be able to use it to its full potential leaving me in a position where I may not benefit much from it.I am the type of person that hold myself to a high standard, which is above average.

The few that do will not provide as high of a LTV and the interest rates are a lot higher than a standard HELOC.

While it is not standard to do this it does happen.  

The one I kept because I found it the most valuable was "Wealth Protection Secrets of a Millionaire Real Estate Investor" by William Bronchick.If you've already got your real estate agent picked out I would recommend asking him/her to walk you through your state's standard residential purchase contract.  

This is typically correct for standard residential mortgages.  

All conventional mortgages should have identical underwriting standards.  

Always confer with a lawyer, particularly one who specializes in this type of knowledge as I have come across ones who are just as ignorant about these laws and regulations. 105 CMR 410.000 MINIMUM STANDARDS OF FITNESS FOR HUMAN HABITATION940 CMR 3.00 3.17: Landlord-Tenant254 CMR 7.00 Apartment RentalsMassachusetts General Law Chapter 186Massachusetts Security Deposit Law: One of the most neglected rental laws in Massachusetts and one of the most disputed between landlords and tenants.

Not sure what B2Rs lending parameters are but you should go talk to local banks and see what they have to offer for commercial loans.Your deal is doable but not shiny by commercial standards.  

Do mortgage rates for FHA/ VA not change with credit score, while the standard 30 year does?