This will be only my second wedding cake.

This bride wants just a 8" and 10" 2 layer for main cake with smooth white buttercream I may be putting on some sort of flower arrangement (fake) and a ribbon around the bottom layer. Then she wants 6" 2 layer cakes just frosted smooth with buttercream.  What would you say I should charge for this?  Since I really wont be doing any decorating?

Charge your lowest base price.  You will not feel guilty after you do a dozen of those 6" cakes.

I have a starting price on my website of $4/serving.  If someone wants a plain cake they pay $4/serving.  The cake you mentioned above is simple so it would stay in the $4/serving price.  But if they wanted sugar flowers, for example, the price of the flowers would be an additional cost.

What is your starting price?  I wouldn't go any lower than that - which is why it is called a starting price.