Hello. Would like to cover 3 separate cakes: 6, 8, and 10 inch layer cakes. All 3 inch pans split into layers,.

I have used the Wilton's 1/2 shortening 1/2 butter recipe but i find it too sweet.

Can anyone suggest a different BC that i can use to frost and make simple decrations, and not too sweet and not too complicated? 

Also, how many cups do i need to frost and fill the 3 cakes?

Thank you

Adding a 1/4 teaspoon of popcorn salt will help cut the sweetness.  Swiss Meringue Buttercream is not as sweet, but a lot more tricky to make, as is cooked Ermine frosting.  

http://artisancakecompany.com/recipe/easy-buttercream/

Lauren Kitchens no cook buttercream......easy peasy to make, pipes beautifully, taste good.

Thank you both for your replies!

MBalaska, how long can i leave the iced cakes out of the fridge? I would like to frost Satuday afternoon for Sunday afternoon event and leave on my counter. 

If not, ice Sunday morning and leave out till the afternoon?

Thank you

Via Lauren Kitchens:

Storage: The day after you make the buttercream you will need to whip at medium speed for 5 minutes. Store at room temp (68-74 degrees F) for up to 2 weeks. (Yes, you heard her correctly). Store in the fridge for up to 2 months. Store in freezer for up to 6 months.

https://avaloncakesschool.com/recipe/easy-and-delicious-lauren-kitchens-buttercream/

my friends, family, and myself have left frosted cakes & cupcakes out on the counter for days...….. it's still lovely.  This is not a business for me.

Thank you so much MBalaska!!!!