I am sure that there are people running V14. They are probably put off by your last question. I do not run V14 but I know how to read and make use of the support.avaya.com site.
Answering in the reverse order posed:
If you put in a V14 CMS you will run into a problem when you have to specify the Adjunct CMS Release on the "system-parameters features" field. A V8 PBX won't let you specify CMS V14 so you would have to pick the latest and greatest V8 supports and hope for the best. Not an optimum choice. Maybe it will work, maybe it won't. The PBX software is designed to support backleveled CMS servers not the other way around.
Looking at the V8 Centrevu Administration Manual (585–210–910), it refers to a maximum of 500,000 agent trace records possible. So why do you only have 28,500? If you have CMS Supervisor, bring it up and go to \Tools\System Setup\Data Storage Allocation\. Three quarters of the way down you should see a line "Number of Agent Trace Records (0-500,000)". This is where you set the number of records to retain. If you don't have Supervisor, on the CMS terminal login as root and issue the following commands:
cd /cms/install/cms_install
vi storage.def
This will let you see/modify your settings.