If you get "trapped" in the cart then you need to "use" it to attach it to you, then start to move and hit "C" to go into combat mode while still moving, this will drop the cart and you should have enough momentum to allow you to get clear.
Floors support each other, as a result you can create a "stepped" walkway in the air that has no visible sign of support, I've used it to create an "arched" walkway from one side of my tribe to the other.
This isn't a "bug" as such as they are getting support otherwise I wouldn't have been able to build them, but I thought I'd report it just in case it's not "working as intended".
The arch you made from floors is fine. All parts are correctly supported, none of the parts are individually floating and the structure is technically sound (so it won't cause any collision or path-finding problems).
I could further limit constrain floors to require four corner support, but I think allowing the half cantilever works alright and allows for interesting structures like what you built.
Corner floors stay red when supported at all corners by posts but can be placed on a single post under the middle of the long side/ the center of what the square floor would be.
Ghosts of items placed on stacked floors stay red.
Floors can only be placed on 2 2x4x2 platforms, not with 1 of them under the center, but can be placed with a 2x2x2 platform under the center.
Ghosts of all posts I tried, with the exception of the Mason Yakitil Post, stayed red when placed on unfinished floors 0.5 meters above the ground and on a finished floor placed on the ground.
After I raised 1 of the floors with it's supporting platform and the post on top of them the post became yellow. Even after I lowered them again to 0.5 meters the post placed on it was yellow and stayed like that when moved to another floor at the same height.
Other posts moved on the raised and lowered floor stayed red.
All posts could be placed on a raised and finished floor although with the actual placing of some, for example the Banaya Weskiim Post, while standing on the floor the Banaya 4x4 truss under the floor got in the way.