There is no one size fits all answer.
If you want to give a run down of the amount of money invested, your expected return, and your risk tolerance. I will take a shot.
If you want my general answer, then I would start by defining an advanced search (you chose your rates and extended credit) that finds 5-10 listings at any given time. Turn this into a standing order.
Then watch the results. Do you like the listings? If so then why? If not then why not?
Adjust your standing order to find more of the ones you like and less of the ones you don’t.
Personally, I have 15 standing order. I don’t have enough money for the loans I find. I just let Prosper (random) determine which standing orders fire when I have money.