Creating tasks to someone assigned in a user defined field

Creating tasks to someone assigned in a user defined field

I'm trying to automate out process, and running into difficulty. I'm trying to have tasks assigned automatically to people along the sales process. I tried to have workflow rules and custom functions to have the potential owner change along the process so that we can assign tasks to the potential owner, but found that to be not possible.

So my question is, can I make a user defined field in potentials to have link with someone within our company ( like how potential owner is)? Then make a custom function to pull that employee and place whoever is in that user defined field and make a task for them? 

My company believes in having an assigned personnel for each customer for each phase. Sales-financing-engineering-customer support. So each customer has a different combination of personnel from each department. If I cant switch the potential owner along the process to the person in charge of the current transition, can I have a user defined field for who is assigned for each transition, then pull that field for task assignments?

I think that is the best way to ask my question.
Thank you,
Matt Laracuente