(Yes, due on sale clause risk, but I've lived with that myself for years without any issues.)3) The equity from the property should be the contribution from the first couple and the second couple should contribute cash such that each party has equal contributions to the LLC.I would definitely have a real estate attorney help you with this as it is too complex for an on-line LLC creator.

The cash flow in the areas you describe can be immense and there are many ways to mitigate the risk.

pay off all credit cards before you even think about investing because for 99% of people the interest you would be saving on credit cards is greater than the investment return you could earn and it is basically risk free.

It's up to you to decide on your risk profile and how much conservatism you want to trade for upside.

Banks get a 50% position this way so their risk is minimal and can get around some of your lack of funds situation.

Scraping and replacing windows (called high risk deleading) are examples of work that would require a deleading contractor. 

Are there any restrictions and risks of renting a SFH for business plus residence purpose?

to spread your risk.  

Maybe put some cash into low risk investments after the Fed finishes raising rates like a 3% CD. 

It's those maniacs that buy homes cash via quit claim deed off of craigslist that really get screwed.Make sure your property manager is a licensed real estate brokerage.Understand you can not eliminate all risk, only mitigate it.