For CB itself we've layout parameters you can use to completely override the registration, profile, and profile edit layouts with your own and insert fields anywhere in that custom layout. This is done from within CBs Default template in CB > Plugin Management under the Layout tab. We include a few layouts or you can just use the Custom one and provide your HTML. CSS overrides are also done from this same location so your custom CSS would also be there.
Template Overrides: Is the standard Joomla template override system the best way to skin the CBPS plan selection page, or are there specific CBPS views I should prioritize?
The standard Joomla layouts are not used. CB and CBSubs have existed before Joomla implemented layout overrides (we've been around for a very long time and we plan to be around for even longer!) so we have our own system. This will change with CB 3.0 and future rewrites of plugins as they're converted to standalone Joomla extensions.
For CBSubs specifically they're just plugins. Notice the rounded template included with CBSubs is a normal fully installable plugin. You can you use that as an example starting point. This will let you override every template file shown in the below folder.
/components/com_comprofiler/plugin/user/plug_cbpaidsubscriptions/templates/default
CB API Documentation: I’ve seen mentions of a CB API, but I’m struggling to find comprehensive documentation. Does the API allow for fetching plan data and category options (CB Options) to render them in a completely custom PHP/JS app?
We don't have a comprehensive API documentation. We're just 2 people and unfortunately don't have the time to write much documentation these days. I'll try to do better in the future, but for the sake of honesty felt I should say our priority is features and bug fixes.
As for API endpoints that functionality has been offloaded to CB Auto Actions, which you can use to create any kind of custom API endpoint you like. It also works with Joomla web authentication tokens for authenticating your auto action API endpoints. CB Auto Actions supports plain html responses and JSON out of the box.
We also include Joomla content plugin functionality that'll let you use shortcodes anywhere in Joomla that supports content plugins to insert CBSubs data. Things like links to the plan, its description, its price, etc.. The shortcodes are documented in the CBSubs system plugin in System > Manage > Plugins.
If you need specifics simply ask what you're needing to output and I can provide you with working examples.
Custom Page via Joomla API: Would it be better to build a standalone Joomla component/page that interacts with the CBPS tables directly, or is there a "CB-native" way to inject custom layouts?
Long term the best option is to just make a template plugin for CBSubs and style it however you like. If your styling can be done entirely with CSS then I also recommend that approach.
krileon
