1. -65dBm for smartphones/tablets.
2. Overlap between two DIFFERENT channels (ex. ch1 and ch6) is good, and especially good when using 5GHZ APs. Overlap with two SAME channels is NOT good, you want to try and minimize co-channel interference.
3. Pretend it's a room, with attenuation values for the walls. You can even create an attenuation area, and use "elevator shaft", within.
4. ZonePlanner can perform predictive analysis on single planes (such as a single floor at a time) only.
If you want two floors (i.e. you want to take advantage of AP reuse from a vertical location), you'll have to make educated guesses. For example, if there is an AP in room 201, and room 101 is immediately under 201, and you have performed an active survey (e.g. using your iphone/android running speedflex and a Ruckus AP), and see that you get 27Mbps and RSSI of -57dBm, then you can predict that a similar room setup down the hallway would be, uh, similar.
I suggest taking screenshots of each finished floor predictive analysis, putting them in stacked Excel cells, and evaluate feasibility of AP placement.
This works well in hotels. Here, I'll share one I'm working with you:
The red circles are just "AP exclusion area" circles I use to help me track where the APs are on the above floor.