Starting before the river “trial” or during it would seem the best jump-off, and we can clearly work with either. For me I think sequential flashbacks would benefit as characters move on the kingsroad. I can go across my version of Joffrey’s thoughts during all of this and watnot.

I don’t think it would be in Cat’s best interests to keep Tyrion in a city full of Lannister supporters when it was KNOWN that she supposedly had Tyrion. By the time of Ned’s “trial/execution” Catelyn was still in the Vale and Tyrion was heading home when he got accosted by the one not-wildlings tribe in the Vale. There’s a lot of distance to travel that we have to account for.

Also are we going by television ages or novel ages?

Petyr has a silver tongue, and Joffrey is still very easily manipulated. So there’s a lot he could do pre-Blackwater. We don’t need Joffrey to be “smuggled out” if he is already obviously fighting in that battle or something. How you plan stuff with Petyr and Sansa is up to you as I have no clue how Sansa is going to be “unbetrothed” or anything like that to Joffrey.

Then there is the matter of Arya/Syrio being approached by the Lannister bannermen when Eddard Stark is imprisoned? Perhaps we can switch that up and perhaps Joffrey goes himself? Hence she wouldn’t be on the run and all of that?