Are you offering collateral that would help mitigate bad credit?

-you will want to review the credit file  looking at how the loan was structured and the collateral file paying attentions to the chain of title on the AOMs and Allonges

He owns 5 2nd mortgages as collateral, owns the house I rent off of him, has bought and sold a few house. 

Since your properties don't have mortgages you could always place one of your other properties up as collateral.   

Here is my full plan; I have a full time job no major debt, great credit score, but no assets to collateralize against.

There are many investors that collateralize this allows them stronger buying power.  

Even then, you would have to get great rates and I don't think you will find  low rates on unsecured collateral.

We have a lot of out of state investors in Tucson scooping up the best deals quickly, so it's a matter of being ready to close on the first deal that makes sense to you before somebody else finds it.Lenders need you to have some sort of skin in the game be it cash in the form of a down-payment, your high credit score in the case of an FHA loan, or other assets in the form of cross collateralization or a HELOC.

Now, my friend expects some kind of security/collateral; therefore, I was thinking of collateralizing through recorded deed of trust on one of the properties that I have recently acquired.My strategy was to completely rehab the property, and then refinance (after 6-months title seasoning required by my US lender) into a long term loan through one of my US lenders, keeping the property as a long-term hold; and through the refinance process also payoff my Italian investor.

At one end is the conventional, traditional lender concerned with capital, credit, capacity, and collateral.