Hey everyone. I have a three tier sesame street cake to make soon and I have a few questions. My cake will be very similar to this:

But the Elmo tier and the Cookie Monster tier will be buttercream. I want to use "fur looking tips" but I don't want both Elmo and cookie monsters fur to look the same (since they don't) beside the grass tip what tip can I use for fur? 

  Also, Big bird with be fondant with feathers like in the photo but I'm afraid that too many feathers may weigh down and cause some (or worse a whole side) to fall off. Ill try to roll the feathers as thin as possible but what can I use that is thicker than water  and not as messy as piping gel to make sure all his feathers stay in place? Thanks in advance everyone!

You can use star tip 18 for pull-out fur.  Also, you could use the small grass tip 233 for Elmo and the large grass tip 333 for Cookie Monster.

If you're gluing fondant feathers to a fondant covered cake, you need not worry about the weight, as long as you roll them thin.  And, if it's fondant to fondant, water will be be a sufficient glue.  However, you can use gum glue if you want.

I did one very similar to that.  I used the grass tip for Elmo and I just kinda swirled my spatula around for cookie monster.  I just used gum glue for the fondant feathers.  Do consider using styrofoam covered in fondant for the beak.  I used fondant and it was EXTREMELY heavy, pulling on the cake and feathers, and had to be propped up from underneath.  I would have been mortified if it were for a paying customer and not my own family.