Hi. I have experience in this area as both an active composer, and also a game developer, so here’s my suggestions, take what you will:-
Q: What are some best practices for small mobile games? Should I ask for a single loop-able track? Or should I request multiple tracks that can be looped?
A: This really depends on factors you should know or decide before your ask for the music, such as, how big you want your built project to be (in terms of MB and in terms of scope - number of levels or situations requiring different music, etc). Also, your budget/arrangement with composer will probably dictate what you are going to end up with. On a technical point, if the track(s) are going to be short (for example, for reasons of a tight budget), but your levels are of an indeterminate length, I’d definitely suggest that you ask for your music to be seamlessly loopable. If the composer is technically minded, and you are able to program this, you could consider asking for musical stems (ie. layers) which can be bought in and out on top of one another, or blocks, which can be arranged in a sequence. This way, you can program the music to grow or progress alongside your game.
Q: How do I explain what tempo I need?
A: It is safest to specify tempo in BPM (beats per minute). ie.
60bpm = is a pulse of 1 beat per second (pretty slow) - a musician might describe this as ‘Largo’.
90bpm = moderate tempo. a musician would call this ‘Andante’
120-130bpm is quite fast, a lot of dance music is typically around this pace. a musician would call this ‘Allegro’
140 - 200 = very fast, ‘Presto’
Q: Is it a common practice for him to create different styles, and for me to pick the one I like most?
A: No. If you take only one piece of advice here, take this:
You should find a piece of music, or multiple tracks that you like, and send them to the composer. Explain very clearly which elements of the music examples that you have sent you like, and why. Believe me, this will save you a lot of time. The only time I would say you might not do this is, if the composer is very experienced (in game music) and has a good knowledge of your project’s requirements - AND you trust them enough to just leave the creative direction with them.
If you can, do try to leave as much of the creative direction with the composer (tell them about your game), depending upon the composer you might find that the most interesting outcomes will come this way (IMO).
Hope this helps.