With the Pro Micro plan, you get 10 new downloads every month. These downloads are not aggregated, meaning that if you do not use all of your downloads in the current month, they will not be added to the next month's total. In the next month, you will start with 10 brand new downloads.
If you reach the downloads limit of 10 icons and wish to continue purchasing more icons in the current month, then you can upgrade to Pro Starter plan anytime. This will give you additional 50 downloads per month. Here you will find more information about How to change your Pro subscription.
The subscription plan is an auto-renewing plan, meaning that you will be automatically charged every billing period (either every month or year depending on the billing option you have chosen). To stop your subscription, you need to cancel it before the next billing period. Read about How to cancel your subscription.
A subscription plan can be cancelled anytime. It can also be reopened after the cancellation. If you only need it for 1 month, do not forget to cancel it before the next billing period is due. You can read about it in this article: How to subscribe to Pro for only 1 month?