Two tips -

1. Get a packard shutter that you can front - mount to the lens. You can control the exposure with the squeeze bulb from your sitting position.

2. For focusing, there's the string method. Put an object in the position you want to be in when you take the photo. Attach a piece of string to the front of the camera. Pull the string to the object, and when taught, tie a knot in the string so that the knot marks the exact distance between the camera and subject. Focus the camera. Then remove the object, put yourself in its place, and then position yourself so that whatever part of your face/body you want to be the point of focus is the same distance from the camera as measured by the knot in the string.