Building a new fighter jet is an example as an appropriate cost plus because if you asked the contractor for a fixed price the contractor would have to price very conservatively due to all the potential unknowns.  

My friend and I plan to buy a property together. I'd be a general partner making all the managerial decisions and only my name would be on the mortgage, while my friend would be a limited partner who would contribute ...

For the cabin upgrades and other items (roof repair, etc) you mentioned you can look into 1 - non-secured line of credit  if you have decent credit history2 - personal loan3 - Check if the seller has equity in the property and see if she would be willing to get a HELOC and roll the balance into the purchase price (this is more risk for her but if you convince her this will be a value add she might got for it.If you plan to rent the property out you will need the appropriate insurance, an umbrella policy will also be a good idea.Make sure the seller knows your intentions; that you plan to rent the units out as STR.

I would just replace X% with "CPI for [insert appropriate area] for [all consumers, or whatever line item you want to reference from BLS reports] as published by US Bureau of Labor Statistics (BLS)" and leave it at that.

There is a third type of money out there, and I think it's more appropriate for what many RE Investing courses and Gurus teach and that's called Private Money or "OPM". 

Aloha,You "just" need to look at everything to make sure it is 1) complete 2) functional 3) secure 4) exposed surfaces appropriately painted/covered 5) not leaking (the single most critical issue to look for!

I am looking for a cpa to help ensure I meet all requirements of a real estate professional, and to utilize a cost segregation study appropriately. 

I thought I was on the right path and I thank you for the confirmation, however the main concern that I had was the appropriate "tenancy" - either traditional lease versus short term rentals such as Air BNB or VRBO which can be spotty few days a month.  

You will need to obtain a license for each property, calculate the appropriate tax, report and pay it.

When done right, investors can purchase a distressed property for a relatively low cash investment, fix it up, and rent it out for strong cash flow.Building equity: One should also account for the amount of equity that is built up during the rehabilitation phase.