Observations on a couple of your queries:

When the block height is wrong, you click the block bar (green section on the left) and then drag the bottom of the block up...or...if the block has a background, select the background and drag to size, the block follows like a puppy.

Dragging objects into blocks. The mouse cursor determines whether the object goes IN the box, or sits on TOP of the block. Drag the object, ensuring the cursor is in the block to insert it.

Have a play with Flexible vs Freehand and Transparent vs Solid Colour