A quick IRR analysis can be beneficial as it paints a better picture of the true "return" of the investment.

I am more interested in building mutually beneficial alliances than just capitalizing on the retail end of real estate. 

It may be beneficial for you to partner with someone and use invest your time in a project versus bringing the needed capital.

The lender said that I could do an FHA for the unit I live in, but would have to take 3 individual loans, or one commercial loan for the other 3 units, which is not beneficial to me.Does anyone know a way around this?

Maybe someone that has a deal and needs a partner, maybe some wholesalers (with reasonable ARV's, lol), maybe someone in a similar position as us that we could join together with in a mutually beneficial deal...So at the risk of getting spammed by wholesalers, lenders, agents, etc, I post and ask for your feedback, advice, referrals, or whatever else you may have to offer.

I would have those extensions be contingent upon a mutually agreed upon set fee.

Do you have any other ideas for tax-advantaged account in which we can buy stocks or mutual funds?

You can always later assign the beneficial interest to an LLC.The trustee however will probably be listed on the deed that is a publicly recorded document.

Flipping to me is a fancy word to use remodeling/construction, in most cases LLC with S corp election would be most beneficial for tax purposes.

Contacting other landlords or management companies that are in your market can be hugely beneficial.