Topsy Turvy Terrible Trash

I have had three bad "cake jobs" in a row...This was by far the worst...I told my husband I am done with cakes..We fought all the way home. I cried and cried...Thinking I have lost something to mess up another cake yet again...
Okay...today I thought I'd ask by buddies on CC for info. I did a topsy turvy for a very affluent couple who are very fru fru...(you know what I mean...everything is perfect). Three tiers, 12, 8, 6, round.WASC. Key lime cheesecake filling made with super thick heavy cream and jello, so it was stabilized...Used about 1/4 inch or less filling...torted. Frosted in buttercream. The Da** bottom layer fell apart. I have done TT cakes before, using the method in Whimsical bakehouse book...No problem, transported fine, lasted at room temp fine...So I tried the method in the tutorial here, thinking it sounded more stable. When I transported, I literally watched the 2 inch perimeter around the bottom layer fall off...Did I use too many dowels...Maybe they weren't perfectly straight? Are my cake sizes wrong. Does my car need a tuneup because it vibrates too much...I'm at a loss...ANY advice tutorials. etc are welcome...I'm at a loss...Help...Before I decide to throw in the towel....

Anybody?!! Please...What method do you use for Topsy turvy cakes....What did I do wrong?

Okay...In the whimsical bakehouse book they do torte and fill cakes, as long as the fillings are thick and stable...so..hm...never heard you shouldnt fill them...As for what happened with the couple..Well I live where the avg. cost of a house is about $160,000. This couple goes to my church and many refer the wife as a diva. She is a dr. and he is a rocket scientist. Their house was just beautiful, perfectly decorated, spotless, and it was easily worth 5 million in this market. I met her at the door and was trying to not cry but I know the tears were squeezing out and my voice was breaking...I said, I am so sorry, I've done these cakes before and never had a problem, but the bottom layer collapsed on the way over here..I said I would by no means accept payment for the cake. (she was supposed to pay me $100). I said I would like to at least try to make it presentable.I had decorated the cake board in fondant in a matching design to what was on the sides of the cake. I removed the bottom layer,filled in the cracks on the sides of the other two cakes, re-smoothed and straightened the chocolate cutouts. I had made a little fondant curled sign that looked like a little antiqued scroll and I set that on the cake and put on a gumpaste "50" on the top and it was at least presentable. the guests began to arrive, many whom I know from church. Several came up to greet me and said "wow" and got the concept right away and didn't know anything was wrong until they saw my face. Then here comes the diva who said to me "make sure you clean up your mess before you leave and walked away..I was so humiliated. The thing is that this person has shown her claws on more than one occasion, so I should have just said no...She is bossy, and many times overbearing...I have always quietly and politely stood my ground in situations where we were both involved so I've never had a "blow out" with her. I have however seen her lay into others. I should have remembered who I was dealing with...
At church the next day, I went to her husband and said, "I really am sorry about your cake, E" He said, "that's okay, it tasted good"...