A major network is interested in buying a script I've written and it
could possibly become a series. I want to know the maximum and minimum
amount of money I can expect for the initial sale as well as the
amount of money I would earn per episode as the show's creator if the
pilot becomes a series. Finally, in the television world as a writer
and creator of a show, what are the most important terms to fight for
in contract negotiations? Pros and cons?

Wow! You're not asking for much are you?
The big answer is... it depends.

How long is your script - 30, 60, 90, 120 min?
Is it original or based on other works?
Dramatic? Documentary? Reality?
The writers guild of america (wga.org) offers a schedule of
minimums for pay which most networks abide by:
http://www.wga.org/subpage_writersresources.aspx?id=68
But shows can be done by a production company
that works with non-union talent - which means they 
don't have to use these guidelines.
Pay can range from $50K to $100K per episode.
But then there are other things like re-writes, polishes and
if it gets picked up, creating a bible, future treatments, etc.

There are really too many variables to give you a definitive
answer. The WGA is where I'd recommend you start.

In answer to your last inquiry, I'd recommend you fight to be
a producer on the show. They have the power to control 
the direction of the show which includes casting. I'd also
ask for a percentage of any merchandise that's developed
based on the show. But that's just a personal preference. 
Call the Guild, hook up with an agent and get the low-down from them.

Unfortunately, what you're asking really can't be covered in a simple
google answer.
hope this helps, though.