You need to figure out your pricing structure so you can justify charging what you charge and be firm. It depends on time, detail, and materials. You can put that right on your website, some people charge more for 'premium' flavors, add on fondant, etc. You need to have an accurate idea of how long it takes you to complete a design before you can charge for it.
I would stop taking orders until you get this in order. There are many threads about pricing and Jason has a pricing website that will help. You can charge by slice or by cake (both should be the same) its just how you want to calculate it. But the actual ingredients don't constitute your price, they should be a factor, but so should electricity, cleaning/shopping/prep time, etc. This is the first thing you should have down before taking orders.
Some detail has to be done in fondant or gp, these are also things you'll need to be able to explain to your customer. Some designs are simply easier or look better in fondant, if they bring you a picture of a fondant covered cake and want you to recreate it in BC you need to be able to explain why (if) it will work better in fondant, but you need to know those reasons before you can expect a customer to tryst in your expertise. It's your business if you don't want to do BC then refer them to another bakery.