You can pause the slide just after all the animations have played by placing an interactive object such as a click box or button on the timeline at that point. The click box will not be visible to the user, a button would be. So if you didn't want the user to see any change to the slide, use the click box, but you may need to add a callout to the first couple of slides to tell your users to click the playback buttons to continue, just to make sure they don't get confused at that point and not KNOW what to do.
Hello and welcome to the forum,
And if you only need Next and Back, try inserting the PerpetualButtons widget on the first slide and set it to display for the rest of the project, you do not need the playbar anymore then. It is not that difficult to create your own navigation.