Just some images to clarify some things and hopefully avoid confusion instead of adding it.
I recommend placing an additional copy of every block you've used/plan to use somewhere on the side of the map to keep track which ones you've already used and how many more you can choose. Delete them before you validate and upload your track.
Signs don't count towards the 9 block limit unless they influence the trajectory of the car. For example, in Canyon signs connected to the surface/offroad parts add bumps which could be used to change the trajectory. If you use them, the sign block counts towards the 9-block limit.
In both examples, the sign alters the trajectory of the car and thus counts toward the 9-block limit
In the bottom right example you finish your run on the multilap block, thus the finish is used as an extra block and not as a finish and counts towards the 9-block limit.
Feel free to ask if you have further questions or anything else is unclear. If you think you found a way to exploit the theme, ask before you build it. Better to be on the save side and avoid disqualification and tears.