Thanks for all of these challenges, my credit score is 790 and my wives is 820, all we have my wives Discover card that she uses for gas and I'm a joint member on it but don't use it, we don't carry a balance, we also have a small mortgage that we pay on monthly, we just paid off the other mortgage. It's totally false that you need 2 to 3 credit cards and lots of debt and pay it down each month, I've found a way to keep it minimal and still have very high credit scores. The only reason I keep my mortgage and one card and pay it off each month is so that we can play the credit score game.
Now if your going to tell everyone that you have to have a credit score to get a mortgage that is incorrect, you can get an mortgage company that does manual underwriting where they look at your w2's and your rental history and base it off of that.
I'd rather not go through that process because I thinks it's easier with real estate investing to have a credit score because it opens up more avenues.