Nothing wrong with your choices, I just think it's more than necessary. But you know your network better than anyone.
I don't know what your budget is, but your costs are getting close to Cisco territory.
If you got the money, Cisco might be a better choice.
Myself, I'm a fan of Extreme switches; better performance (expecially with QoS) and costs less than Cisco.
Note that the diagram I provided is for clustering, not stacking.
Stacking can only be done within the same family of switches. You can stack the 5500s together and the 4500s together. Stacking also requires a special stack cable.
For clustering, you can either use fiber (need SFPs) or copper (preferably CAT6).