An assuming buyer may not be as credit worthy as the previous borrower.

Also, since most RE is depressed now, there are plenty of good areas to invest in that are cash flowing, and you can find creditworthy, tenantworthy applicants.

The amount you can take out on a HELOC is limited by the equity in the property used to collateralize the loan and your creditworthiness.  

As far as the credit worthiness of the buyer.  

Debt Service Coverage Ratio loans do not consider the credit worthiness of the borrower but instead considers the income potential of the property. 

Or because of the credit worthiness of the borrowers?

The biggest thing that confuses me is how to make your entity credit worthy enough you personally do not need to guarantee loans. 

These deals are highly dependent on the creditworthiness of the tenant.  

Sure there used to be a time when underwriters used the FICO as the sole determiner of credit worthiness.

Now that you have paid down the balances on the cards and depending on your overall credit worthiness you may want to look into the possibilities of leveraging credit cards to make "spreads".This is possible through 0% credit offers now available on most cards.