Hi Paul this is a Brass Forum so you are unlikely to get useful advice on Saxophones however for what it's worth, Chinese instruments are now much better than they used to be and anything that Conn/Selmer put their name to will be better than the cheaper unbranded models.
A secondhand American...
Try contacting The Librarian at Kneller Hall, that used to be the best way to obtain copies of Regimental and Corps Marches.
There are contact details at the bottom of this page Royal Military School of Music
Not exactly "On Topic" but whilst browsing I came across this article about one of the Finest Tuba Players who (probably) never played a Compensated instrument. I found it an interesting read... hope you do too...
Most of my music at www.pdfbrass.com will work without any percussion. Any "Rythmic" tunes will always benefit from a decent kit player but it is not always essential.
Feel free to email me if you need any advice on suitability email@example.com
What mouthpiece are you using ? The Bach and Yamaha mouthpieces tend to be rather narrow rims. If you can find a Neill Sanders they have a wide rim which may be more comfortable - although at a slight loss of flexibility.
PHC (Paxmah Halstead Chiddell) mouthpieces also have wide rim options.
Playing F Horn is hard enough. Playing with braces is even more difficult.
You will struggle.
The advice that I give to my pupils is to play what you can and not to worry.
When your braces come off playing will be easier again.
PS I know my profile photo shows me playing Cornet but...
Indeed the G22 was supplied with B&H cornets in the 1980s as I recall it was stamped on several different models and I don't think the number/letter meant anything other than that it would fit a cornet.
If it works for you - use it !
In my ,humble, opinion, the ability to write for those of us at the lower end of banding and still provide music which is satisfying, listenable and which provides enough of a challenge without being beyond reach, is a true skill - much easier to write for those who you expect to be able to play...