If you plan on modifying the dimensions of a feature, do not override tools on the library object. Stay with the automatically selected tools. This allows the automatic tool selection to modify the tooling when the dimensions are changed.
If you want to create a single library part that contains more than one object, use a group. If you want to ensure that the operations of that group are not rearranged, check the Ordered checkbox of the group.
Any object type can be added to the part library.
If you want to use a unique name for your object, rename the object either before you put it in the library, or rename the object in the part library.
Center the object around the origin. This makes it easier to place the feature when you paste it into a document.