Just about ready to launch this baby.... Was wondering what is best for a first campaign. Will be promoting newsfeed posts on Facebook.
Which do you suggest:
IMO, id rotate 1 offer over a few networks
The more variables you test the more $$ you need to spend, there's heaps already on the forum about that. But, I would test as many offers as you can afford even if it's at the expense of one of the landers.
The offer can/will make or break your campaign and you can't optimize the rest of your funnel if the offer is a dud.
In terms of 1 network or several depends on your cashflow. Cashflow is king. If you're not already on weekly payments or meeting thresholds, focus on one network as much as is reasonable.
Good luck 
1 vertical, 1 traffic source. You can test different deals in the same demographic + vertical. But don't branch past that. As Pawly said more variable = more money spent.