Questions from a beginner

Hello. I have been exhaustively researching home lighting automation systems Philips Hue, Belkin WeMo, etc). I have never heard of Lutron, so I have spent the better part of today researching their products. But there are a lot!

I would like to start this project by doing small spaces but I had some questions:

1) Caseta seems great for most of my needs, but the general consensus seems to be it's designed for areas, and not whole-home automation. It does have some features I want, such as Honeywell wifi thermostat and Logitech Harmony hub integration. Can I mix this system with RA2 or is it one or the other?

2) RA2 seems like it's the more agile system, but also more complicated. Would this system integrate with other hubs?

3) I would like to start with closets and do one room at a time. Would either Caseta or RA2 allow this kind of expandability?

4) I've looked at dozens of sensors, it seems like a wall or ceiling mount motion sensor would be most appropriate for small closets/pantries with the light switch on the outside? The motion sensor specs look like WAY more than I would need for this kind of application (18 meters if I remember correctly).

5) Eventually I want to move to kid rooms with vacancy sensors. Would either ceiling or wall-mount suffice? What would be the advantage of one over the other in this application?

I am technically inclined as far as home networking, IP cameras, hubs, and basic home wiring go. I expect a learning curve, but expect to pick up on the automation part quickly. Just need some information to get started.

Thanks in advance.

I'd recommend you check out the training materials on Lutron for RR2 training or an RR2 installer, which will give you a sense relating to your questions. That said:
1. The systems can't be mixed generally speaking
2. RR2 is integratabtle into about everything, but it does require hands-on integration if you don't go with items already set-up for it. For example, you can use the Roomie remote system, and a number of alarm systems, etc.
3. I don't know a ton about Caseta, but I believe the answer to both is yes. RR2 obviously is more expensive to do this, but it's also much more expandable. When I did my personal system, I started with exterior lighting and then added over time
4. If you just want to do closets, where your switches are located is important (i.e. if they're on the outside of the closet, sensors at the switch don't make sense). Again, I only know RR2, but I think Caseta uses the same sensors: http://www.lutron.com/en-US/products.../overview.aspx The aren't switch mounted sensors and they work very well. I suppose you could ignore a system all together for closets and just go with the cheap-o wall mounted switch combination occupancy sensors. It's not as nice as the full system, but for closets, it might be cheaper.
5. Ceiling is the best because you can cover the whole room. In my garage I have a pair of them so I can work on a car and be seen when I would otherwise be obscured.

Caseta cannot be easily mixed with RadioRA2. It is possible if you deploy bridging devices running software like IFTT. The overall performance (triggering, delay, dimming) will not be as good as having a system entirely based on RadioRA2.

The main advantage Caseta has today is that it is HomeKit compatible and better integrated with other devices (via the Staples hub) while RadioRA2 is not (yet).
It almost seems as though Lutron is attempting to capture the market (for the low end & DIYers) using Caseta while RadioRA2 is positioned to serve the high end where systems are usually specified and installed by official representatives.

Possible rationale for going with RadioRA2
1. If your system will be spread out or have more than 50 devices, RadioRA2 is the way to go (It does get pricey).
2. Another possible reason is that the look and operation of the RadioRA2 switches is still better than Caseta.

Tidbits
Both RadioRA2 and Caseta can be hooked into an Alarm.com security system.
RadioRA2 occupancy sensors can be programmed to act as vacancy sensors for specific periods of time.

The deciding factors for whether to use a ceiling or wall mounted PIR sensor should be coverage and the likelihood for false triggers e.g. - people walking outside the intended target area being picked up