For basic warmups, I would include a lot of the stuff you do in concert band. Good tone is good tone. We do lip slurs (from the Foundations book) daily in both concert and jazz. We do scales in "swing style" - play each note twice, in swing 8ths, up and down one octave. That's a line in the red book that introduces major, mixolydian, minor; I extend that into several keys (start with Bb, Eb, F so you have a Bb Blues).
Instrumentation - for starters I would bring in anyone who wants to play. Clarinets can read a trumpet or tenor part off the page. Flutes can read off the piano or guitar. Euphonium is easy with a trombone part, tuba can read the bass part and transpose an octave. Horns are a different animal, you'll probably have to teach them to transpose (easiest is from alto sax) or re-write parts for them. The EE series has a horn book, so at least for the method book you can get them going. I can see the argument to honor the tradition of the art by limiting it to only traditional jazz instruments. If I had instruments to loan I might get some of those kids working on learning new instruments, but for right now I take what I can get.
If any of the kids on non-jazz instruments play piano, get them on a set of vibes. If they dabble in guitar at all, they can learn bass.
Once you get into playing charts, you won't often find parts for clarinet or flute (except as doubles on sax parts in more advanced music) and almost never for horn. There are a few Woody Herman charts that use horns.
The biggest thing you can do, for both you and the kids, is LISTEN. Take time out of every rehearsal to listen to some great jazz. We do a lot of listening to professionals play the tunes we're playing (even if it's not the same arrangement) to imitate style.