Also keep in mind that even though the rate is higher on that second mortgage, it's on a fraction of the value of what it would be if you refinanced the entire thing.

Even then, in Europe the degree to which their dorms or frats resemble the  “Animal House” or “American Pie” type experience is a fraction of what it is in the states. 

a retaining wall behind the garage install siding repair drywall add a full bathroom in the baseman open a new egress window and finish the basement talked to a Spanish roofing crew and replace the roofing for a fraction of the price and paint the interiors fenced the back yard What was the outcome?

It is done differently in different states I believe but in Virginia where I live you can do either percent of square footage or the fraction of bedrooms you do not occupy divided by total bedrooms.

Worst case you learn a life lesson with a fraction of that cost, so you gained knowledge, experience and broaden your network,or not so worse, breakeven (so the cost would be your time and labor), you gain knowledge, experience and broaden your network, or better you make money and increase your net worth while still gain knowledge, experience and network. 

Are you and the other $15k lenders on one fractionalized note (if legal in NJ) and, if so, who will manage that note?

With rates where they are today if you are not going to house-hack there are other ways to place some money into real estate that are more indirect (i.e. fractional shares, REITs, etc.). 

I can tell you that design is only a small fraction of the time spent on a project.

To me, with the advent of the internet in the 1990s, all of this information is available for free or a fraction of the enormous cost one pays to Renatus and STILL has no license to do much of anything except write more checks if wishing to invest.

The investing discussed on BP is only a tiny fraction of the real estate investing marketplace.