Yep there are a lot of wires, but if you want to do this you are going to have to get used to that. Unfortunatly the one wire that is there is wrong, it is connecting a signal line to ground and needs to be deleted, the ground is in fact on the other switch lead (I rearranged the switches at one point). While there really isn't an easy way to make the breadboard connections, the one I find most useful is to start on one pin (for instance the left most switch after you delete the black wire that is there now) and highlight it and move along it a bit. That will create the wire to its first connection point (in a straight line) now (and this is the tricky part) avoiding clicking on any of the other rats nest lines (or more usually, using the delete wire dialog to remove new wires to get them out of the way) route that one wire in a reasonable way to its associated other end. Then pick another one and do the same until they are all done. The created wires are easier to see than the rats nest lines and the created wire will route to where it should go.
This looks like a good place to start, it is simpler than your original circuit and should let you get the rest of your connection chain solid before trying your original circuit. You will want to correct the connection problem before trying much more. The last thing you want when making a new circuit is to not know whether your new circuit isn't right or you have a cable / connection problem. You need to have a solid connection to your midi device so the only unknown in the path is your new circuit. I don't know much about midi but it looks like this is just an RS232 serial connection to your Mac. The most likely problem here is a speed mismatch between the Arduino and the USB midi converter. There are a set of standard speeds that serial cables run at and if you have a mismatch then the connection either won't work at all or gets errors which makes it work sometimes. As noted you want to get this corrected first so this section of the path is solid.
Peter