The two main building units for Rubble City are the Long wall and Short wall. Individual, other pieces vary widely in size and shape but you can get a good feel for dimensions by comparing those pieces with the two standard walls.
Long wall is 120mm long by 57mm tall and 12mm in width.
Short wall is 90mm long by 57 x 12mm.
Of course! The Pledge Manager will provide you with a personalised code to the value of your Pledge - you can then use this to select specific Unlocked items from the menu, and can add any extra pieces you hadn't decided on previously - as well as anything from the wider Fenris webshop catalogue, should you want to maximise your postage savings!
Postage will be calculated based on the final combined weight/volume of your finished Pledge in the PM.
Don't see the answer to your question? Ask the project creator directly.