There is a wealth of information in the realtor’s statement “he did not want to do it right because of the amount of work involved.”
There is a series of questions listed. I will try to address each one.
A good skylight is a very pleasant addition to any home. There are many very good skylight manufacturers that have solid warranties. A good handyman with the help of an experienced roofer can properly install a skylight that will give you many years of enjoyment.
I cannot imagine a skylight that would be an integral part of your structure. Removing the skylight and installing rafters and sheathing, etc. will make it stronger, not weaker. Question #4 removing the skylight would have no effect on the integrity of the roof structure.
Generally speaking, it is far easier to remove a skylight than to install one. If you have a curb mount sky light that you want to keep, I would strongly encourage you to do so. Check out the type of mount you have and pick out a skylight that you would like. Have your roofer give you an estimate to install with a warranty for his workmanship and also from the manufacturer. Bear in mind that the leak may be some place not related to the skylight.
Often times, when a skylight leaks, it is a temptation for the homeowner to try to seal the leak with some type of roof mastic. A good roofer can usually find and fix a roof leak before any serious damage is done. And if the leak is in the skylight, the easiest, least expensive repair is to replace the skylight.
I hope this little bit of information helps you make a decision that will let you enjoy your house.
Best Regards,
Your Friends at AskARoofer