Has anyone ever attempted a separated tier cake with pillars with the cake sizes being 8", 10" and 12" in size and 5" tall each? I feel like its going to be huge, heavy and almost impossible to hold its weight on the support rods that are going to be in the cake. Here is a picture of what the bride wants. I told her I would ask my favorite people in the whole world, then I will give her an answer. ;-)

This is similar to what she is looking for. Thanks everyone!

I have made many cakes that size .  Be sure to use plenty of  dowel rods or bubble straws to support the tiers. I would use at least 8 on the 12" and 6 on the 10". Lightly  press the cake plate 10" plate centered on the 12" to leave a faint inprint. That will show you where to put your dowels within that circle. Do the same for the next cake.

Thank you so much! @mahtc2016

The cake which started my journey into decorating was this size.  As ignorant as I was, I had no issues.  It only had one set of separators because part of the second one was lost.

That cake (the picture of what the bride wants) has no additional internal support rods (dowels). It isn't a double plate system which requires support rods, but rather a single plate separator where the pillars are actually the support system. Each pillar has a floating/sliding ring that adjusts to the cake height so it looks like a pillar, but it's actually a spike that's inserted all the way through the cake to each bottom board.

There are several SPS system brands that are available -- here's an example:

https://www.wilton.com/9inch-bakers-best-disposable-pillars-with-rings/303-4001.html#q=pillar&prefn1=contentType&prefv1=shop&start=6

@Sandrasmiley That is such a cute cake. Im feeling a lot better about this one. @CWR41 I was wonder how there were no plates at the bottom of each pillar! That is really cool. I think I will give that a shot! 

Miss.Reynolds, this is an old Wilton pillar set, but I think they still make them.  The plates have little nipples that fit up inside the pillars to keep them in place.   I did use dowels inside the tiers to support the ones above.