OmniFocus doesn’t use numbering at all to delineate task order — though that’s something we do offer in OmniPlan, which is more commonly used for project management.
That being said, we do definitely support setting up a specific order for your actions by way of the Sequential project type. When you set up a Sequential project/group, you’re telling OmniFocus that all the actions in this project/group need to be completed in a predetermined order. You could then a filtering option like First Available to only show you the next available item at any given time.
If you need to reuse this list over and over, you might have better results when setting the entire project or group to repeat, rather than setting repeats on the individual actions inside that project. If your entire project or task group is set to repeat, once the whole project marked as complete, then another iteration of that project will be created with the same set of actions—in the same order—you previously specified. More information about the project types can be found in our User Manual.