What do you think is the best way to approach making a 3d van 9x13 or 1/2 sheet cakes and stand them up or stack them? Thank you in advance for any advice!

Definitely stack them. There's no reason to turn them sideways when they'll be far more stable stacked.

Thank you I'm only doing three layers I was thinking about doweling also I baked last night and tried the wasc recipe but it doesn't seem denser and one of the layers is already breaking apart it is for tomorrow bim stressed!