I've done it plenty of times and it was fine. What I would do is hammer a sharpened dowel into the cake to keep it from shifting.
I make mile high cakes.....like 7 inch hummingbird..etc....I think you would be ok...if not heavy on the fondant....maybe roll the fondant just a tad thinner...OR even if you use a white chocolate fondant that can be rolled thinner....less likely to break the cake. BUT...Merissa do you really need our advice?? YOu are REALLY good!!
I admire your work!
It depends - if I can separate it easily I do, or if it is not too big I just leave it on and cut away.