What is the latest version of CB for these Joomla and PHP versions?
We still support Joomla 3.x so all current releases work for it except plugins specifically designed for Joomla 4 and 5 (e.g. like our new CB SEO plugin). CB 3.x will be dropping Joomla 3 support though so it's certainly worth migrating.
What are your recommendations regarding CB with addons when migrating to current versions?
Ensure CB is completely up to date before migrating and you shouldn't have any issues in regards to CB itself.
We went from J3 > J4 > J5 all in 1 shot. It was relatively painless, but we almost exclusively use our own products so we didn't have a bunch of other extensions to contend with and CB has robust backwards compatibility so was never an issue. We first reverted to default Joomla template, uninstalled the old template, uninstalled Kunena (it has no backwards compatibility bridge!), migrated to J4, cleaned out old J3 extensions that are no longer marked system extensions, migrated to J5, installed Kunena, and applied our custom CSS. There's a lot more steps specific to our site mixed in there, but that's the basics of what we did. It went very smoothly and took no time at all.
krileon
