I have about 1 wheel per 2 gliders. but if your cage is big enough you can always add more, specially if they us them.
You could try a whiffle ball filled with fleece strips,
or I hear tie a loose knot in a long fleece piece and hang from the roof of cage.
but I think one of the biggest things is try to get 3 sets of toys and cage stuff, and switch them out every week. this will keep the cage fresh and different for them.
a few dried mealworms in a few foraging cups in different spots in cage will keep them interested.