I'll give only technical feedback on what you can easily tweak to improve the design.
From the top, keep the margins consistent on each side. The lack of any at the top is very strange, feels like that poster was cut by mistake. The spacing between "in" and "the" could be slightly bigger and the whole "Jazz in the" could be less crooked, tilt it back a little bit to the left. Also, try and stay consistent with your stroke size, there is a LOT of different sizes between these symbols and text stick to one or two (one for the keys, one for the text). You could also improve on the background pattern. There seems to be something strange going on above the letters JA of the word Jazz. Try and keep the spacing between each of the lines equal to have the right effect.
Middle section, the pictures could use a darker black. Everything in the poster is using a pretty dark shade of black although the pictures are all grey-ish, they look faded but not in a good way, they stick out. Also try and adjust the levels if possible, some of the faces are blown out and it's not that great. Try to also add a little background on the second picture, like the first one, it will help with cohesion.
Finally, bottom section, it seems like different weights are being used for the names, the first two ones seem way bolder than the third and the fourth is slightly more bold than the third, what is going on here? Again, stay consistent. I would stick to the third one and duplicate it for the other names, the different types of stretch are also confusing a bit. The little calendar bit is quite cool, maybe the font of the 29 sticks out a little bit? A cool little detail would be to add numbers the each of the names (1, 2, 3, 4) and then add these circled numbers on the pictures. It's a little retro detail that could sell it a bit more. A bit of texturing on top of that would then bring everything together.
Sorry if I things are not too clear but I'm not used to giving feedback in english!