Different anon. If the Vale did join the WoFK for the Starks, would they be looking to form their own kingdom or just serve under the King in the North’s?

But would the River lords still acclaim Robb king? I assume the Vale would want it’s own independence, but would they divvy up the Riverlands with the North?

Discussed here and here. 

The Vale coming in on Robb’s side really changes the politics of that post-Camps council at Riverrun, because they would be a large contingent of socially conservative lords who don’t owe Robb a debt in the same way that the Riverlords would, and Robb would need to keep them onside because they’d be a plurality of his army.