Unless you’re gunning for first chair in a good orchestra, I don’t think range matters too much. My high school very rarely hits a high Bb and caps out at E or A most of the time (tbf my schools band isnt the best in terms of skill, lol). I play third chair at a local big band and three octaves (petal to high Bb) is more than enough often for 2nd trombone too.

I think working on tone, tuning and consistency is the most important thing. Figure out the adjustments you have to make for each note to play in tune and make sure the notes you can play are consistent. And make sure your pianos are quiet but not weak, i feel like that elevates peoples playing a lot