Planes and Cars themed 2 layer 8 inch and a 1 12 inch bottom, do I need to add a support or can I just stack them up on one another?

I am using a yummy whipped cream (with cream cheese) frosting that is pretty sturdy ( added con sugar). Was thinking of using that jarred marshmallow stuff as the clouds, what do you guys think??

And the pavement, I was thinking a sugar sheet or maybe just cookie crumbles. I had an AWFUL experience when I attempted my sons 1st bday cake. It was traumatic! lol. So this would make for that one hopefully. 

The dye I am using is wilton. But I don't have much experience at all using dyes. Is there a brand that does not turn your mouth and lips the color your eating? I hate that!

Just about all dyes that are used in sufficient quantities to make a dark color will turn you lips/mouth that color... some even with pastels... it is dye after all... most here - to my knowledge - use americolor...

I would definitely suggest supports in the bottom tier... no matter how short... I wouldn't risk any collapse or sinking...

Someone else will have to make suggestions on the clouds... 

I think the sugar sheet will look more like pavement than the cookie crumbs would...

Since I don't know your icing, I can't help on any questions you have with that...

that marshmallow fluff stuff is a bit unruly -- you might want to tame it with a bit of icing mixed in --

if you pipe it to look like a cloud regular white icing will do it for you too -- i like to outline my clouds with a bit of pale blue -- just like smeared on there to give a shadow effect --

real fine chopped oreos should make a nice black street looking surface --

good luck -- give yourself twice as much time as you think you need -- 

AI made pavement by rolling out candy clay. Get the black candy melts so you don't have to use the wilton black dye. Just search modeling chocolate recipe or candy clay recipe. There are few on here. It's pretty easy, but you need to make it at least one day in advance before you roll it out.