It depends on whether “further animations” means the same Actions will be used/repeated or whether they will be new ones. You can reuse the same Actions over and over again just by add ing them as Sequence Strips (I don’t think there’s a limit to how many instances of the same strip you can use).
If you want the objects to make different animated movements (transforms) from those in the existing Actions then you have to keyframe new Action(s). Unlink the Active Action by clicking the X in the Action Editors header, then “Add New” and start keyframing from frame 1.
It helps to do a StoryBoard beforehand, then work out which transforms can be keyframed as seperate Actions ie: atoms join to form molecule = 1st Action; Plus Sign moves to position = 2nd Action; Plus Sign moves back and forth = 3rd Action etc… then all these seperate Actions can be converted to Strips in the NLA Editor (some of them multiple times) and be arranged to animate in the sequence in which they will be rendered.