I am needing to concatenate two custom fields into the address field through a before insert trigger. Will the before insert trigger fire before lead assignment rules?

Hi i am working on lead conversion.I need to override the standard 'Convert' button given by salesforce with VisualForce page and write apex code for it. I need help in the following

1. There are many fields(Standard/Custom) in lead that need to be mapped to Account,Contact and Opportunity custom fields. 

2. I have a picklist field 'Commodity' on Lead screen which has values 'Gas', 'Electric' and 'Both'.

If 'Both' is selected on Lead Screen then 2 Opportunity records should be created one with Commodity as 'Gas' and another with Commodity as 'Electric'.

Please help me achieve this functionality.Thanks in Advance.

I am needing to concatenate two custom fields into the address field through a before insert trigger. Will the before insert trigger fire before lead assignment rules?