I have the opportunity of joining a group of mixed children and adults all brass. It is a spin off of a successful town brass band. I already play piano grade 5ish. I thought that as I can read music already I just might stand a chance of keeping up with the kids learning wise!!! What are my chances? I have been told most people start with a cornet and move onto other instruments as you progress.
As a teenager I tried to teach myself trumpet, from a tutor book (in the 1950s). It was difficult, and I never made the progress I had hoped. Later, I went on to learn drums from a professional teacher. I played drums for forty years - pubs, clubs, student big bands, Old Time Music Hall, annual pantomimes and all the 'standard' musicals, barn dance bands etc.
Most of the valved brass instruments use similar fingering I think; I once understood trombone to be the easiest to start on - maybe it doesn't need as much 'puff' as trumpet.
So, as you already understand music, I should think it is a reasonable goal.
I add below a link to an excellent county music service: