i have little time with two little ones to bake and make frosting and then frost the cake. last year frosting was the hardest part.

Can i purchase a plain frosted cake at the store (is it self crusting buttercream that they use?) and decorate myself?

Yes. but if you want to completely cover with fondant the frosting will already be set... you can do accents just moisten the designs with a little water or tylose glue

Yes, it will work.

thank you! i will probably just do accents but this will be awesome! my husband is deployed and organizing/handling a bday party alone is so much work that i just cant spend two days baking and frosting the accents i will make with fondant and gumpaste way ahead (air tight kept) and then just plop em on

Sure u can use a cake mix. If you want a more dense texture add 1 additional egg, about 1/3 water and 1 cup flour. Works for me when I'm in a pinch for time. No complaints yet....

You can mist the icing with water in a spray bottle, then you can actually still cover the whole cake in fondant