If you are not going to puree the tomatoes in a blender, you can skip peeling the tomatoes the skin will not go through the strainer. Peeling is necessary when you are using a blender as the blender may puree the skin in a way that the strainer may not
The ketchup can be stored in refrigerator for 4+ months.
If your jar lid is metallic, the ketchup may turn blackish.
I prefer to use brown sugar for ketchup. You can substitute brown sugar with regular sugar if you want.