First I have a question about your stand. Have you double checked to make sure that your boards will fit on the stand without falling through? It sounds like you have a good variety of sizes, but you definitely want to make sure before you have to set up the cakes.
As for how to finish off the icing on the other cakes. I don't do much with marzipan (I'm assuming it's similar to our rolled fondant here which has no taste to it). The way I read your comment is that you are putting on sugar paste flowers, correct? (Sugar paste isn't what we consider an icing over here--just for decorations.) If that's the case, then you definitely want to put an icing on the cakes to seal in the moisture. As for the carrot cake, I would just use the same icing as the other three (buttercream?) because if you use the cream cheese icing, it will have to be refrigerated until you are ready to serve it.
Just to give you an idea, here is my schedule when I am doing a cake for a Saturday wedding (and yes, I did my own wedding cake):
Wednesday--start baking my cakes. Once they are cooled, I crumb coat them to seal in the moisture and crumbs (plus I don't have to ice the cakes right away if they're crumb coated)
Thursday--continue baking my cakes and finish the baking if at all possible. I usually try to have the final coat of icing on all the cakes, too.
Friday--day to decorate.
If you would like an idea of what I use for buttercream icing, I'll gladly share it. An easy way to get a smooth finish is after you have put on the final icing coat, let it sit for a couple of minutes ~10 - 15 max (but don't let the icing completely set up) and then use a paper towel (or wax paper) to smooth out the icing. Simply rub your hand with some pressure over the towel on the cake. The key to this is the type of paper towel that you use (wax paper or similar can be used, too, but I've always used paper towels). We used a brand called Viva. We have found that the cheaper the paper towel, the more texture (like a golf ball) you will get on the icing. Viva leaves a smooth icing.
I'm not sure if I actually answered your questions very well

but I'm more than happy to help in any way I can. I actually have to start baking cakes for a 2 tier wedding cake for this weekend today--a 12" round half spice & half yellow and an 8" heart in raspberry. Now to just figure out what I'm going to put in between the tiers....