I am trying to create a formula that will seach for installers in an area (defiled by the mailing address zip code)

I need it to look at the zip code for the Person account Mailing address and based on that populate a field (Field type does not matter) & could just be displayed even on the Opportunity Page. 

The other trick is that based on how many instalers I have in a zip code they are stack ranked 1-6 with 1 being the installer I would most like to use.  In addition to this I need to know if (based on a credit report that I run outside of the SF application the installer will work with customers within a specific credit range (I.e. 600+ credit all installers take, below 600 but higher then or equal to 525 only some installer will take.  So I need to be able to display both to my sales rep.

Example:  Customers zip code is 80110.  In that area I have 5 installer all take 600+ credit, so I need to display the #1 dealer in that area, I also have 3 that take credit scores of below 600 but higher then or equal to 525, and I need to dispalay that as well to my reps.

I am NOT a programmer, I'm an operations guy, but I can follow instructions (If they are detailed)

Any help would be apprechiated.  I already have my zip codes and dealers associated and ranked in an excel file.

Scott