This is my first brass instrument

Hello peoples. So I’m 21 and haven’t played trombone since highschool. I’ve really wanted to pick it back up for a while now but don’t really know where to begin.

Im currently in my first year of community college and wanted to try and get good enough to get into the symphony band at my school. I don’t own a trombone yet and I’m super rusty. My school also offers private classes that you can take. What would be the best course of action to take?

I got a "big kid" trombone later in my musical life, and I still don't know a huge amount about it. Can you play stuff higher than C3 with the F attachment, or is there some problem with that?

I ask because I'm playing a piece in community orchestra with a phrase that would be way easier if I could play D3 with the trigger in (I'm still clumsy at disengaging it quickly) but no position chart shows any trigger stuff above the C3 partial, which makes me think it isn't something people do.

What tips do you all have for a lifelong trombone player looking to get better at tuba for professional jazz and theater gigs? I’m especially interested in any air ideas or mouthpiece tips. I play on a Hammond 20BXL on my bass right now.

To keep my embouchure in shape, i got 10 feet of tubing and my mouthpiece and brought them on vacation. (I really don't like just buzzing on the mouthpiece.)

Since it's not conical, the partials are all very stretched, so it's terrible for intonation. A funnel on the end didn't help.

I got bored with bugle notes, so I cut a hole about 11% of the way down, so i could get a whole step. (That's 2^(-2/12) for you math and physics people).

It's 3/8 inch ID vinyl tubing.

When i got back from vacation, i still sucked at trombone.