Thanks, yes the measurement will take into account the eye level. Thanks for the suggestive answers to question 4. For question 2, do you know of any way that the angle of elevation can be measured more accurately apart from taking more measurements?

Use a stable tripod to measure on level ground, mount the clinometer on the tripod. Improve the clinometer to include a laser rangefinder so you can measure the hypotenuse and adjacent side easily. The distance and angle values will be more accurate.

Not sure if my answer is in syllabus as these are cheap modern tech that you can find.