Akeeba Release System
First of all, Akeeba Release System will manage the downloading and releasing of your plugins.
You will need to create a user group and a view access level for each plugin file (an item of Akeeba Release System), where downloading this plugin file is allowed only for users with the corresponding user group and view access.

Akeeba Subscriptions
On the other side, Akeeba subscriptions will manage the payments and subscriptions, you will create a subscription level for each plugin, each subscription level has 2 actions:
- Add to Joomla! user groups: Users will be added to these Joomla! user groups when their subscription to this level is enabled.
-
Remove from Joomla! user groups: Users will be removed from these Joomla! user groups when their subscription to this level is disabled.
The level is enabled when a user finalizes the payment for it, and disabled when it is expired or cancelled for any reason.
So, Akeeba Subscriptions will handle adding/removing users to Joomla! user groups, and Joomla user groups are having view access, also Akeeba release items/files are controlled by view access, so only users having a valid subscription will be able to access and download the plugin they paid for.

Akeeba Ticket System

Here are some cool features supported by Akeeba Ticket System:
- Nested categories at an infinite depth
- You can turn off replies / new tickets (with an optional message)
- Private and public tickets
- Attachments support
- Credits system: charge per ticket type or per reply, integrating with Akeeba Subscriptions
Also, it is important to know that Akeeba Ticket System is NOT a CRM.