Dimensions for dryer vent hook-ups from floor, and size of vent from dryer to outside. Does it all have to be the same size?

Most dryer vents are 4". Vent material will depend on whether you have a gas or electric dryer. Whatever the size of the oulet on the dryer is the size you should run to the outside.

I agree with Dad77. In addition: you should not reduce vent. It should be 4" all the way to the outside. Dimensions for dryer hook up differ from dryer to dryer. There is really no set dimension.