Assuming you're thinking of the Oneworld Explorer ticket (and not the less popular Global Explorer ticket), it may be worth your while reading the Oneworld Explorer Guide wiki

"...and relay my route to the BA operative.."
Absolutely, just have everything ready.
In the past I have simply fed the agent:
Date From-To Flight Number
for each flight I want
The agent takes all that and passes it to the airline's Fares Team who verify compliance with the rules and price it.

As for the Base Fare, what's your starting point and cabin class?