I don't have any NEW info to add. But, I'm just now feeling comfortable stacking cakes. So, I know your stress level.
Try not to tighten up about it. It'll make even the smallest things difficult. Here are some "calming thoughts" I use for myself.
(1) It's helpful to me to think of each tier as it's own cake. The bottom tier will be on some sort of base, right? So, picture it as you designed it...just the bottom tier on the base. Stack, ice, complete as normal. Set it aside. Repeat with all tiers. THEN, go to doweling.
For me, "hunking" out tasks makes it easier for my brain & nerves to handle.
(2) I apologize for not double checking where you are located. I had an "issue" with sweating. I had a very cool cake & a very humid day. Not sure how fondant works. And, I'm not trying to panic you. Just trying to help you cover your bases. I'm sure there are topics here on CC about it. (our weather here in Ohio has been nothing short of bipolar....this is why I mention it)
(3) TIME....TIME....TIME!!! Work ahead like everyone is saying. If you have your buttercream process down & you have time on your side........it'll be just fine!
(4) Enjoy! This goes with #3. Gotta have enough time to actually enjoy the process. Try to take pride & put some love in it.
You'll do great. My last adventure was a SpongeBob cake. I have come a LONG way. I did notice I had more fun with that one.
AND, more time.