That depends on your workload, but really autogrowth should only be there for emergencies not as part of the plan. You should size tempdb (really all your databases) to what you need for your load. In your case it looks like at max load you need at least 30GB, so that should be the initial size of the database and, if that is all the space available, it shouldn't have autogrow on. If you have more space then, based on the information you've provided, I'd start with 1GB growth. But first I'd put some monitoring in place to track usage and an agent alert that fires when I reached a set % used (probably 80% in your case) so I could check what it using the space.