You might find it a useful exercise to grab a major gear vendor's catalogue (
Boston,
Martin,
SDP/SI, etc.) and pick one series of gears you're likely to use during the next season—and model it for yourself. That way you have a model that you know works well with your CAD software, and which doesn't contain any potentially undesirable simplifications (as many gears available online do).
First, start with a basic design with as much detail as you need. (Years ago, it made a lot of sense to avoid
modelling individual gear teeth, when the pitch circle was more or less sufficient; nowadays it isn't that much of a problem, because computers are much faster. Your choice.) This will give you a good feeling for the features of common gears, and which of those features are well-defined in catalogues (and which, like chamfers, aren't). It will also give you an opportunity to learn about CAD support for things like material properties.
Then build yourself a parametric model of that entire gear series. In Inventor, Pro/ENGINEER (Creo) or SolidWorks, you can build a family table of associated parts, each representing variations on the same basic design. When you need a part, instead of downloading a new one each time, you just pick the element directly from your table—and can switch between table members without resolving part dependencies.
For example, 32 (diametral) pitch, 20° pressure angle gears* are commonly used in the first stage of a custom gearbox using RS-550 motors. Boston's YP series and SDP/SI's S1084Z-032 series are good candidates for this sort of practice.
*0.8 module, 20° pressure angle gears are very similar to 32 pitch gears (not identical: 31.75 pitch), and in FRC applications can generally be run together with minimal ill effects. (Not ideal, but far from the worst gear mismatch that teams have gotten away with.)