Question:
1. I noticed in project properties that UTM indicated '???'
2. Is there a way to import a master benchmark after having imported the topography data or does it have to be done all at once?

Answer:
The first point in the imported file is taken as the Master benchmark.  Tools > Project Properties will show you the location of this point then you could enter the lat long for the point (Note. This change is not saved when you save the osd file and exit due to a bug).  Then export to agd file and get reasonably close coordinates but be careful becasue '???' in UTMZone actually means a local coordinate system based around the MB. This coordinate system is slightly rotated compared to UTM (approximately 15m horizontal difference over 1km).