The latest version is r14 SP2, which DOES support a direct upgrade from r12.8:
Upgrade and Migration Considerations - CA Client Automation - 14.0 - CA Technologies Documentation
According to the support matrix, r14 SP2 does also support Windows 2008 SP2 (with or without R2):
https://docops.ca.com/ca-client-automation/14-0/en/supportability-matrix
ITCM upgrades are performed, over-the-top, starting with the Enterprise, then the Domain(s), then Scalability Servers, and finally the agents. r14 SP2 does have an agent auto-upgrade feature to help automate agent upgrades, to lessen the manual effort required, so I would look into that.
Also note with the r14 installer, whether your MDB is local or remote on each manager, you do not have to run the MDB upgrade separately, as you did in r12.5 versions and earlier. When you perform the upgrade on the Enterprise or Domain application server, it will reach out to the database, locally or remotely to apply any database schema changes.
Let us know what further questions you have. Once you've upgraded to r14 SP2, I would reach out to support, and obtain any recommended patches.