The Personal plan gives you 5GBs of SSD storage.
For the Premium subscription plan you get 10GBs SSD storage.
The Agency plan gives you 40GBs SSD storage.
As for surpassing the given limits - you will be charged an extra $1 for each 1GB extra space you used at the end of the billing month.
For a more complete list of the pricings and advantages of each subscription plan, please see our pricing page.