Ryan, I’ll add my opinion ...
The Stanley 4, 5, and 7 are the three bench planes that count most. Take some time to clean them up and tune them to work as best you can. Remove all rust and, if necessary (if they are pitted or very out-of-flat), replace the blades with Veritas PM-V11. Get a second blade for the #5 anyway. Camber one for removing waste, and a straight one for short jointing and narrow edges. Learn to use the chipbreaker to control tearout (David Weaver wrote a great
article on this). It is possible to turn these planes into superior performers.
I’d get a better block plane. It is a very useful tool for small areas, such as chamfering. If you are trying to keep costs down, look at the LN #102. If you can stretch the budget, the LN 60 1/2 or Veritas DX60.
Many have suggested a LA Jack as your second plane. I would do it differently in your case. A LA Jack is a good plane, and useful for a number of tasks, such as shooting and jointing. I would recommend it if someone was starting out with fewer planes than you have. At this stage I would use your #5 (with a straight blade) or the #7. Either will do a good job as long as the blade is sharp (that should go without saying).
I also would not recommend a shoulder plane. Mortice-and-tenon joints are among the most common joints you will make, but I am not a fan of planes in tuning either shoulders or cheeks (as it requires a fair degree of skill to avoid tilting the plane and removing more waste than you want). The one exception is a router plane, since it will ensure that the cheek is parallel to the face of the stretcher. I would use a chisel for both shoulders (push a medium chisel into the scribed line) and cheeks (use a pencil for high spots and and remove with a wide chisel).
The plane that you most need right now is one for rebates and drawer grooves. So, the Veritas Small Rabbet Plane can do both. Or, look out for a vintage Stanley #78 for the rebates and make your own wooden grooving plane for drawer sides.
Regards from Perth
Derek