Fondant lace will stick to crusting buttercream but you need to apply fresh buttercream to the back of the lace pcs. to get them to stick. You can freeze the cake all decorated but defrosting it properly is the key. Box the cake tiers then wrap the box in an unscented garbage or plastic bag. Two days before you are traveling with it, remove it from the freezer and put into the refrigerator but keep the box and bag on. Then the day you're delivering, take the boxes out of the refrigerator and let come to room temp. Any moisture resulting from the freezing and refrigeration will form on the outside of the plastic bag. Then remove the bag and open the box.to finish the thawing process. Yes, this is a long drawn out procedure but there's no other way - other than not refrigerating. Some of my friends just put a plastic bag over the cake when they take it out of the refrigerator and make sure that the bags opening is pressed tightly against the counter or table it's on. Hope all this helps. Is buttercream sturdy enough? - I guess it depends on how thick your lace is and how many pcs. you are putting on your cake. I honestly don't believe you'll have any problems. Just make sure you crumb coat well so that the icing is really stuck to the cakes surface. Brush off your cake surface before crumb coating for best adhesion.