It's all about the notes you choose and their rhythm and configuration, and whether the piece is successful or not depends almost solely upon that. It is still best to determine your instruments first, but truly, your general notion of the piece should already be directing you to make the correct choices.
Instruments and instrumentation are 'neutral' in conveying much outside of badly worn cliches which are always best avoided. There are good arguments both for and against using the now cliche 'minimalist' orchestration of multiple malletphone ensembles (multiple marimbas, pianos, keyboards, etc.) as well as for using any of them -- they sound well and 'work' for the style.
Instrumentation is often chosen first by what instrumentalists will readily be at hand, available, and able to perform to the level of technical demands of your composition.
Ex: If you have certainty there will be two pianists, a 'cellist, two violists, a soprano saxophone player and two clarinetists readily available, then there is one very ready answer. Dependent upon the level of their ability and ownership of a second instrument, any of the reed players might double on another reed (clarinets I and II might each alternate to a Bass Clarinet and an Eb Soprano clarinet... and if you have the luxury, the pianists might also double on a celeste, toy piano, and / or play digital keyboards, allowing an additional array of timbres including electronics.)
I would avoid literalism in your choice of notes, configuration and instrumentation: it is death to any worthwhile imagination, including that of your audience.
Best regards.