credit limits

is there any credit gurus here who can advise on this? im currently in a midoffice role in a startup physical commodities trading shop, currently looking into devising a credit policy from ground zero for my firm. credit risk management was never considered until recently, so there is no existing infrastructure to build on, no default data, ratings, analysis, or limits. what kind of data would you consider in defining the firm-wide risk appetite and some sort of "house" limits? i am thinking a combination of management input, budgeting plans, book capital...then allocating that to the various trading desks. a crude and simple approach...but im not exactly trained in credit risk. any pointers or directions?