When installing vinyl flooring, if you want to avoid a step from one room to the other, bring the lower floor up by adding plywood under it. This works in certain cases if the flooring underneath is hardwood. In this case the client did not want a threshold so I went ahead and added half inch plywood on the lower floor to make it the same level throughout before installing the vinyl flooring.
When opening drywall up to do repairs or to access behind the wall, use the same piece of drywall you cut out to put back in. Bevel the edges before taping and compound or the edges may be proud which would cause more compound to be needed and more labour to achieve a flat surface.