The plus membership costs $14.99 per month, and is renewed automatically unless you cancel, so no, you don't have to do anything. And if you run out of connects before your membership is renewed, you can purchase more.
Do you have any payment method added to your account? You can easily buy connects anytime. Just go to Membership & Connects and simply click on buy connect option. You will see a pop up menu from there select the details and fill the form.
The amount of connect you buy will instantly deposit in your connect balance.