Yes, just keep it regrigerated and then let it sit out for about 15 minutes before whipping it again to freshen. You can also add a little splash of milk or a tablespoon of confectioner’s sugar to adjust the consistency at that time.

Overmixing will cause the frosting to deflate, break down and become soupy. It won’t hold its shape anymore for decorating and just slide off the cake.

Well, then it won’t really be buttercream. It will have a waxy mouthfeel and you won’t have the flavor of the butter if using all shortening instead. So if you are trying to adhear to cottage food industry laws, you’d be better off buying the shelf-stable buckets of frosting from Costco.

You can use whatever you prefer. I tend to use slated because it cuts the sweetness just a bit – but it is really a preference thing.

It really doesn’t matter – whatever I have on hand. Sometimes it is generic, my mom always used Crisco. But now living in Hawaii, I can’t always find exact brands.