Most pieces in the "community band" repertoire will not go below F2 (just below the bass clef staff) or above Ab4 (three ledger lines above bass clef staff). As Dave mentioned, some marches will go up to the Bb above that, but in most (if not all) cases, you could bring that down an octave if needed.
Just for fun, the highest and lowest notes I have encountered in the band euphonium rep are an Eb5 in Kevin Houben's "The Lost Labyrinth" and a Bb1 (pedal Bb) in Grainger's "Children's March".
University of Miami - BM Euphonium Performance '21
Indiana University - MM Bass Trombone and Euphonium Performance '24
Besson Prestige 2052S
Courtois 551BHRA
Conn 88HCLSGX
Various Greg Black mouthpieces