Well I'm not sure I'll be of much help, because when I made my son's minion cake (you can see a pic of it in my photos) it was my first attempt at a lot of things (stacking a cake, fondant). However, maybe some of the mistakes I made can help you.
First, keep it simple and don't use any fruit fillings LOL I would like to attempt fruit fillings in a cake again but not until I get better at cakes. I always made cupcakes and these yummy fillings, and tried to transfer that the first time I made a 'real' cake to serve to people. Well, maybe I overfilled, maybe I didn't support the cake well enough...I don't know. But my cake definitely slid and kind of went lopsided on me. I made it work but it was stressful. I have tried it twice now and it's done the same things both times.
Second...I used 3 6" layers, and a 5 3/4" half-sphere layer for the rounded top. This worked really well. However, make sure you use strong supports (like wooden dowels) to put through the cake. I used straws (why?? I thought I read it somewhere! LOL) and that did NOT work.
Finally, for the fondant work...I made MMF for the very first time with this cake and while it worked really well for this cake, the second time I made it, the MMF didn't come together. So maybe it's tricky or maybe I flubbed something up...I haven't done any since those 2 tries so I can't say for sure. But, if you are confident in your MMF skills or have time to try out a few batches incase the first doesn't work (it's cheap, and keeps for quite a while so if you have time this would be a good idea) then I would definitely do that. If you can't do it or don't want to make your own, just don't buy Wilton fondant. Yuk!
I did have some issues with my fondant tearing, but not too bad. My problem was I rolled it out WAYYYYY too big, and the excess fondant hanging off the turntable was what pulled down and made mine tear. If I did it over I would measure my cake and try to roll out only a little more than necessary so I didn't have all that weight pulling down.
The other thing I would suggest is for his bibs - make a template somehow. I free-handed mine and while it looked ok, it wasn't great. I would definitely sketch it out or something and use that as a template for cutting my fondant before I did it again
All in all though - it's a fun cake to make and even though mine looked a little worse for the wear, it got TONS of compliments and gives a big wow factor!
Good luck, and post pictures!!