+1 to all of that. The beauty of the thing is that the value starts to really become more realized as you add additional functionality. Yes, every module adds a bit more cost. But the majority of the cost is in the base unit itself and the energy bar.
One lesson I've learned the hard way in other projects is just to get the "best" you can right up front if there's ever any question. Agree with Reduck totally. I feel like the Apex Jr. would really be more frustrating than anything. It's just enough to get you to the point you'll go, "Jeez, I wish I'd just gotten the full thing. Now what do I do with this Jr.???"
Here's a nice comparison chart over at TB Aquatics.