Questions about overlay solid timber flooring

Hi all,

I'm reaching the end of my reno and have a few questions about an overlay floor.
I am looking at 130x14mm solid Tas Oak, laid over yellow tongue board.

1. Should I glue and secret nail?
2. The floor will be running into a tiled surface which is roughly 15mm higher than the yellow tongue. Should I instead opt for 19mm overlay and sand down to be level, or should I instead use a cork or other underlay to bring the 14mm up to the height (or would the glue make this 1mm difference up anyway)?

Cheers!