I would like to know how I might be able to change ......

Draw your floor using "Create rooms" tool in Plan(Main menu).
Then double click or Plan->Modify Rooms and apply your texture by importing it.

Is there a tape measure tool anywhere ....

Plan-> Create dimension can help you with 3 clicks.

How can i create a second floor within the same design ...

Plan->Add level then draw your 2nd floor.

See the official help to work with SweetHome3D ,
and don't forgot to watch the video.
[:-$] .