If you’re on the Pause and Build plan you can still add apps if you like and the subscriptions would be the same as if you had a fully opened store.
With the $9 plan, you will be charged monthly, have access to the admin and be able to install apps. Your storefront will be paused and you won’t be able to process sales. It’s a good option for a merchant who is setting up their store before launching.
With the full pause plan, which is free, you will not have access to the admin and will not be charged. This expires after 3 months, after which time you will be automatically switched to the Pause & Build plan for $9/month.