Wedding cake advice

Hello baking experts. I need wedding cake advice. My friend is getting married in early August and asked if I’d bake her cake. I told her I’m just a hobby baker and I’m not good at decorating. She’s fine with that.

So she’s requested a three tier cake for 60ish people. I looked it up and it seems I’d need tiers of 10”, 8” and 6”. I’m thinking of getting some dowels and cardboard bases for each layer.

For the cake, her favorite has always been pillsbury chocolate box mix and that’s what she wants for the wedding. Along with canned vanilla icing. How sturdy is that cake? Is it good for stacking? And is that a good icing to decorate with? I was thinking of baking the tiers in advance, icing between layers and freezing them. Then I will assemble at the venue and ice on top. I’ll have about 2 hours to do that.

It would probably be a 2 hour drive to the venue with the cake in a cooler. I’m thinking it will defrost enough to stick dowels into by the time I get to the venue. Right?

Please help me plan this. Thank you!