Sorry if this sounds redundant or too much theory... but I believe it’s critical to understand.  

To clarify.. time signature does not relate to tempo.  In fact, the one has nothing to do with the other.  Time signature tells you how to count the beats in a measure.  Tempo is simply the speed at which the music is played.  A piece of music may be played at any tempo, regardless of the time signature of the piece.  

BPM is one way to measure and set tempo.  Some music will have this notated.  Suzuki, and most other teaching manuals do not note the tempo that specifically because the teacher should set the tempo based on the speed best suited for the student, although for learning purposes, a noted range of tempo is noted so the student may learn how specific types of music should be played.  

Composers will note tempos to give the piece specific emotion intended and will place various tempo changes throughout a piece as one of the ways to evoke emotion. 

Tempo is no less important than time signature, but the two are fairly unrelated and should not be confused.