Jonathan
Spider has answered the main part of your question but in answer to the rest of it, you will find a variety of different North Arrows and Compass Roses at
http://cadblocksforfree.com under the category Drawing Elements.
You should draw the scale bar at full size as part of the house plan. It will then always be in correct proportion to the house whatever size you print the drawing at. For example, draw a horizontal line 10 metres long with 100 millimetre high vertical lines at 1 metre intervals along it's length and add text 0m, 1m, 2m, 3m, etc.
Mike