Your advice is good. However, I would advise looking west of Nineteenth Street. If you want a classic twin feel or a single family home, the area between Tilghman and Hamilton from Nineteenth to Cedar Crest is a solid bet.

The one and only area I'd look at row homes in Allentown proper is right along West Park on Turner or Linden Street.

Bethlehem is ok if you stay on the North side.

Emmaus is a small, old town and it feels like it. The western end of the Lehigh Valley is lots and lots of expensive subdivisions and then it opens up to very small farming communities and towns.

Source: I'm old and grew up in the Lehigh Valley. Went to Emmaus HS.