A CBSubs plan can only maintain 1 usergroup at this time unless you use the below usage with CB Auto Actions with a Usergroup action will allow plans to maintain as many as you want. By maintain I mean give and remove a usergroup based off their subscription status.

Plan Active
Triggers: onCPayUserStateChange
User: Automatic
Access: Everybody
Conditions
1: [var3] Equal To PLAN_ID_HERE
2: [var2] Equal To A

Plan Expired
Triggers: onCPayUserStateChange
User: Automatic
Access: Everybody
Conditions
1: [var3] Equal To PLAN_ID_HERE
2: [var2] Not Equal To A

Giving a user a usergroup does not create a new view access level. It simply gives them that usergroup. A view access level is a collection of usergroups used to determine view access for various aspects of your site. You can have a view access level per usergroup if you wanted though I suppose.

See Joomlas documentation for further explanation of view access level and usergroups below.

docs.joomla.org/Main_Page

How you setup your usergroups and view access levels is up to you depending on your needs. Giving them usergroups is trivial and CBSubs can do this among other things like CB Auto Actions.

do you see any potential problems in a set up like this?

Yes, you're creating new parents with no permission inheritance. This isn't an issue if what to setup permissions (literally everywhere) since they'll be inheriting from Public they initial have no permission to do anything. I recommend the below instead.

- Registered
- - Free
- - - Bronze
- - - - Silver
- - - - - Gold

This means Gold has all the permissions of Silver, Bronze, Free, and Registered. Please understand this is strictly permissions. It does not mean access. Access is controlled with view access levels.