Creo does not provide a means of patterning geometric entities within a sketch.
You can pattern a completed sketch. The only times I've done this is when I wanted to have reference geometry for features.
Generally speaking, the emphasis in Creo seems to have been on patterning features. Make a simple (or not) initial extrude, revolve, etc. Then pattern that to get the grid, circular array, etc. that you need. There are a lot of different ways to pattern things, some of which are pretty sophisticated.
To be honest, unless I intend to use a sketch for multiple features, I don't see the usefulness of making a sketch, then making the feature. It needlessly doubles the number of things in the model tree with no obvious advantage. I think the only reason people are taught this method is because that is how it is done in other software. Not a compelling reason.
As far as mirroring goes, you can mirror things in a sketch, I don't know if it's required in the latest versions, but I always use a centerline to mirror geometry in this fashion. They are also extremely useful to define symmetric geometry. You can mirror features, too, but I try to limit that to only when I really need it. Again, I don't know if things are better in the latest versions of Creo, but feature mirroring has proven to be kind of quirky in the past.
