I gotta agree with Azreal on this one. Understandably you are putting rules into place to protect yourself, but you know how it all works.
I have ONE large loan that defaulted, and unfortunately it only took one for me not to loan anything out more than 500pts. I don't do loans through the marketplace, since there are no safeguards.
If this works for you, that's great. If it doesn't, well, you'll know why.