Q. I need three commentaries on Luke's Gospel? Which commentaries should I use?

Probably the best place to start is the New International Commentary on the New Testament on Luke by Joel B. Green. It is substantive while not being too technical. The footnotes provide pointers to other helpful resources. 

A second choice would be the Word Biblical Commentary on Luke 1-9:20 or Luke 9:21-18:34 or Luke 18:35-24:53, all by John Nolland. These are much more detailed than Green's commentary but contain significant amounts of technical information. These also assume you can read Greek, though you can use them profitably without knowledge of Greek. In addition, there are copies of this commentary both in the Stamps Theology reference area and in the stacks. The latter may be checked out. 

A third, much-less detailed but still helpful work would be the Abingdon New Testament Commentary on Luke by Robert Tannehill. You can find additional commentaries on Luke's Gospel by doing a subject search on Luke, Commentaries in the APU library catalog.