Carpenters who do rough construction get very proficient at "close-enough" measuring. For example, to quickly draw a line parallel to the edge of a board, you can place a pencil at the end of a combination square and move both the square and pencil along the board. Some combination squares have a hole in the blade for this purpose.
Here's how to remove painted woodwork for refinishing. Score the paint with a utility knife to prevent splitting the wood. Gently begin to separate the wood using a dull chisel or flat bar. Then use a stiff putty knife and a prybar to remove the woodwork. Keep the putty knife behind the prybar as you work to avoid marking or denting the wood. Proceed carefully to remove the whole piece.
Low grade stainless steel screws and nails will sometimes stain the surrounding wood.