Not sure the best place to put this, so hopefully this is okay.

The kosatka prep mission can sometimes be the one most likely to go wrong, due to the higher risk of dying. The longfin prep on the other hand can pretty much be skipped by using a phantom wedge and job warps to teleport the trailer straight to the drop off. Removing the police can also be done as soon as you collect the trailer by accepting an apartment heist invite, making this mission very fast and easy.

On the finale you can choose the main docks and drive round to the drainage tunnel and enter there as normal. The only limitation I can think of is then not having the scuba suit, making swimming slower.

Perhaps this has already been tested and I'm just not aware. Sorry if that is the case.