Depreciation cycle doesn't need to absolutely mirror when the gear is removed from service, but you need to look at your failure rates to determine when those costs are going to exceed the value of leaving old equipment in the field. It gets pretty pricey when you start impacting the users.
Pretty sure the resellers we have here don't exist south of the border. Your vendor relations folks should be looking for VAR's that can offload a lot of the work your IT department would need to do in provisioning new Apple gear. In terms of clients to integrate them - we used enterprise directory software to integrate the credentials of our *nix/Mac and AD systems.
" It would have saved intolerable years many videos/data engineers suffered in enterprise environment. My last employer has about 1PB of backlogged data."
You'd need to be a bit more specific on this use case for me to provide some feedback.
