Dear sir (or ma'am), I love lots of questions in numbered form. It's like a checklist!
Your questions are very similar to the Guaranteed Delivery from Particle Cloud to Particle Device thread from earlier today. In that thread, he's asking about publish/subscribe (pub/sub), but the end goal is very similar.
- Not yet. However, it's on the feature list, but I'm not sure what the priority level is yet. There was recent news from another product that may include what you are looking for. See the quote below this list for more info.
- I personally don't know of any solutions off the top of my head, but I wouldn't doubt that it has been done before. As an interim solution, see my response in the thread mentioned above.
- At this point, you might be rolling your own solution, so you can do anything you want there!
- See answer #2 above.
- You can use pin or timer interrupts to wake the device from sleep, but there is no way to wake it from wifi. Part of sleep is turning wifi and the cloud connection off.
- Check out the Spark Battery Life Testing thread. The Photon consumes less power, so you could consider those timings in that thread as a worst case scenario.
DigiStump is working on their own wifi device, called the Oak, that runs on the Particle Cloud. One of their touted features was "persistent events". This is a small quote from their newsletter that went out yesterday (2015-10-30):
Things like storage and persistent events are being developed by the Particle team and are being pushed out between now and January.
Since that isn't directly out of Particle's mouth, don't take it as gospel. It may only be initially rolled out for Oak. I do know that both companies intend well for their users, so don't get discouraged or anything. Plan for the worst and hope for the best!
I'd like to ping @dave on this one for corrections/clarifications. This feels like it might be in his area of expertise. 