I'm making a 12", 9" and 6" square tiered for Sunday. It's white cake with strawberry puree and white chocolate ganache, so it's a little heavy. I tried to find the sps but no one had square. From all the stories I've heard, I don't want my first cake to keel over. I have to find some other way for support.

I thought of getting a cake box of some sort so if it tried anything, I could maybe contain it to a small problem.

I need your professional opinions - how many dowels do I need (I got the long plastic ones) and what else should I do to make the cake secure, both during transportation and carrying?

I'm so, so nervous about all this. Thanks for any help you can offer.

A good rule of thumb is one dowel for every inch in the size of the layer. So 12 in the 12" and 9 in the 9".

I use the wilton wooden dowels and have never had a problem,

im pretty sure the wilton site has a guide as to how many to use. mmm, i did look, and maybe not.
some people like to do a main central dowel, feel it gives more security (sharpend, and stuck right through - many posts on how to do this).
some people like to transport the cake chilled (to be at room temp when served tho preferably, and if you are pretty sure it wont cause problems - like colours running - experiment first!).
just remember, over doweling will damage the cake its self, meaning the dowels arent supported, so your cake is more likely to have problems. id say a dowel an inch is overkill.
if you put 9 dowels in the 9 inch cake to support the 6, they are all concentrated in the middle - thats a lot! i would probably go for 4 or 5 dowels. in the 12 inch layer, to support the 9, maybe 6 to 8.
xx

For next time, Oasis Supply usually does have the square plates, but truly, you DO NOT need square plates under a square tier. A round SPS plate works fine!!

SPS came out with square plates not all that long ago, and for years and years we just used the round plates.

For cakes that small, I use 4 in each. That's been my rule of thumb for decades and it's worked fine.

Too many dowels can turn a cake into swiss cheese and can damage the structural integrity of the cake. If you've ever cut a wedding cake in which another baker went overboard with doweling, you'd understand what I mean. The cake I cut that had uber-doweling was the messiest cake I've ever cut, and it was because there were big dowel holes every other inch. The pieces were crumbly and unattractive, and very hard to handle & deal with.

It's a good reason I highly recommend that bakers cut 2-3 of their own wedding cakes a year, so they can see firsthand how their assembly affects the disassembly and the serving of the cake.

I thought of using the round plate, but they didn't have the size I needed and the pillars weren't the ones that lock in for a snug fit as I read here.

Do I then need a center dowel through the entire cake?

Should I use royal icing between tiers?

Should I check the cake with a level after I put on the 9" cake?

Someone suggested putting the cake in a sturdy box that's used for moving with the opening on the side so it can just slide out easily. I go thru the entrance and then down a couple flights of stairs.

Anything else I need to know that I haven't asked?

I apologize for all the questions and I feel kinda stupid. Please bear with me as I learn.

no reason to put RI between layers. I use a center dowel hammered down thru all layers and I also only use about 4 o 5 dowels per tier. always check for level before you stack and as you stack