Ambitious! I wish you luck with it, it’s always good to have more options. Just as an example, I’m an edge case because I’m quadriparetic, so NFC never works well for me. I can’t hold the phone to begin with, let alone position it appropriately. But again more choices is always better. 
Most of the logic that you described cannot be run on the SmartThings platform. It just doesn’t do that kind of stacked conditional logic well. It also has very limited persistent state variables.
But what some people do, and some have very sophisticated systems, is to run a separate server, anything from a Mac to raspberry pi, do all the stacked conditional logic there, and then just issue the device control requests to SmartThings. Most of the projects using various Wi-Fi presence were using separate servers.
The Reboot Problem
I personally don’t tend to design occupancy around Wi-Fi on phones because then whenever someone reboots their phone you get a departure and arrival event. And people reboot their phones a lot, even if they say they don’t. That’s the advantage of a device like an IBeacon or the Zigbee arrival sensor: they really never get rebooted except when the batteries are changed once or twice a year.
The SmartThings Zigbee Arrival Sensor
I am unfortunately one of those for whom The Zigbee arrival sensor just doesn’t work well. I worked as a network engineer, so I have a pretty good understanding of the various issues, and support worked with me for several months. It didn’t help. There’s just some local interference, probably from my neighbors boosted Wi-Fi, that causes my arrival sensor to continually lose contact with the hub. So it goes. There are other people for whom it works great.
A Two Device Approach
The following topic describes how I ended up approaching the occupancy issue using two separate devices to address the arrival sensor’s flakiness. I’m now using Ibeacons in the mix, and I’m really happy with it. But the receiving station app isn’t on my phone. Instead, the IBeacon is attached to my wheelchair, and the receiving station app is on a tablet at home that is always plugged in and serves as my home automation command center.
So again, different things work for different people. 