See, I think it's the pi's that are old and redundant, the android has lots of things the pi doesn't have like a backup battery and a built in touch screen, plus access to all of the cool google services :).

The rule engine can run on anything that supports java - linux/windows/mac, so it'll probably run on your NAS and it does run on a pi. For setting up the rule engine and for remote access even through your router you need the android version (it's how I manage licensing), but it'll run in an emulator as a client to manage the server or as the server if the emulator has Google Play and GMS.

Google Drive comes as part of your google account (which you get when you have gmail and you need to get the app itself from Google Play) so I'm pretty sure there's nothing more to set up once you're in that deep...

The pi is far from redundant, it has no battery so needs no backup although it's not hard to rig a battery pack up. Touch screen can be added so to be fair it may not be ideal for something that relies on androiD services but it was designed for education and has a huge variety of applications it can be used for. It all depends what you use it for, but redundant? Hell no.

As for android devices, they are designed to remove control from the user so Google can have their way with your data unless you root them and something I get annoyed about is the distinct LACK or battery backup. Devices now come with embedded batteries, then that dies so does your fancy 600.00 phone.

Thankfully I still have one of the last Samsung phones with replaceable batteries.

I meant redundant as tongue in cheek, teasing back to your comment about the android device as the weak link... Sure, for people who prefer linux the pi is a fine choice. Kind of expensive though, esp when you add the battery, touch screen, and power. An android phone with all that is < $30 from bestbuy and the battery is replaceable if it's ever necessary (I have automation for safer charging). Either will work with my app.

One advantage is that same android device can then be used as a central console for home automation - my app has a pretty comprehensive set of widgets for single touch control. As well such a device can display time, weather, calendar/schedule, thermostats, cameras, security system, etc, all of which can be customized and the device itself can be upgraded as they improve. For example I have tablets upstairs and downstairs for easy access including touch and voice - they respond to google assistant commands as well. Old phones are good as replacement switches - I've one in the kitchen that's converted a single switch for 4 lights into a customized display now with 4 separate widget for each light.

The pi is excellent for automation and you have more direct control over it than the constrained android environment, but it does need extras to make it really convenient and more skill to setup.