Clouds come in all sizes, scale not that specific. The important thing is to not do anything that is too bold. With back ground representations we generally are seeking a cohesive diaorama. A slightly overcast sky w/o any specific cloud formation could provide a nice setting. Fade the colors toward the bottom to show distance.
Consider, if a new visitor would walk in and say "Hey, nice clouds", it may be over done. If the comment is "wow, nice RR", then you nailed it.
However if this is to be a toy like bright colored Plasticville busy busy heavily populated platform then anything goes.
It's all good.