@Diego Figueroa I'm in the middle of two small subdivision projects (4 homes and 3 homes, respectively), but they're in urban San Diego City proper. 

Vacancy should be projected to at least cover one month of rent.  

@Adrian Aguilera, my guess is that if you buy where you want to live, it'll hold its value at least as well as your current home, and your vacation rental (providing that you buy a project/discounted home that has all the potential that you need).

The main problem in Pittsburgh is that we have very few 1 level houses without 15+ steps up a hill that would actually be suited for the projects, mostly because the properties that would be well suited are too expensive to merit the rehab expense (unfortunate that our population is old and our housing isn't suited for them). 

Residential property is more about control due to circumstances, personal preferences, cash flow, equity build up and debt pay down...holding for term and exiting with cash...Why are you investing and what do you hope to accomplish with this project? 

Jack,IRA LLC is not a DIY project, you should use a professional who can set this up correctly.

For example, if the proposed project estimation total is 90K, can a group of investors invest 30K each, each gaining their fixed interest on it based on their contribution?

Scott’s book The Book on Flipping Houses, I am finding that this strategy is very similar to being a project manager and managing the triple constraints (cost, schedule,performance), which I enjoy. 

I have a HELOC I use, and two lines of credit, but I use them for short term projects.

Peter if you go new subdivision pay attention to the size and solvency of the builder.The small builders that do one off homes or small to mid size cluster subdivisions those are the ones that usually can be in big trouble if an economic shift happens.Look at new build permits coming online for the area and the price range you are looking at.The big builders tend to be more experienced and can still finish out  projects with down turn so you do not get left with a pipe farm development where some homes and some empty dirt parcels.Nothing is foolproof but this can help.