X4500 if you looking to replace there is different options :
1. are you looking Modular ( you can look Cat 9400 as replacement)
2. best option cat 9500 and you and add more as required based on the port densiti requiremet.
3. Cat 9600 depends on feature rquired here - but quite expensive.
Migratin plan :
1. how is your exiting network - what is the role of Cat 4500 ( core / dist) - Layer 2 only or host any Layer 3 ?
here is plan high level.
1. Build new Cat 9XXXX with stack wise virtual
2. connect to exiting Cat 4500 (layer 2 or Layer 3)
3. Move the access Layer switches 1 at a time toi new one, keep monitor
Note : make a small network diagram for your understand and migration plan, share here, so people suggest what best, i given high level approach, there is nut bolts need to calculate as per the plan.
