SIC Code and an Index Title next to it:  For example:  3291 Abrasive products

I am currently planning to use a Multi Select field and have someone type in about 400 SIC Code values with titles.

The problem is that many manufacturers we are wanting to qualify leads with have multiple SIC Codes.  So we would like to have Industry 2nd field with the same exact look up values.  We may add more fields if some of our target accounts have five SIC Codes then we would want five fields so that we can easily search for other companies in our territory (in the Leads module) who are in the other SIC Codes.

I'm not a dbase designer, just a sales guy.  So I'm not sure if this is the right way to solve this problem.  

My questions are: If I create multiple select fields, can I paste the values from the first one into the second one or do I need to type them in one by one?  Secondly, would it be better to have a look-up field of SIC COdes and reference that in each of the Industry Fields?  Thirdly would I be able to search for companies that have matching SIC Codes for the one I am interested in no matter which of the fields it is in? (For example:  If ABC Company's first SIC Code is 3291 and ZCorp's third SIC Code is 3291....could I do a search that pulls both of them by matching 3291 or do they have to be in the same field?