Customer Account
There is a Maximum number of 2000 Sites per Customer.
There is a Maximum number of 1000 Jobs per Customer Site.
There is no Maximum number of Jobs per Customer, just per Customer Site.
However, even though the product will allow this many Jobs, you won't be able to open the customer if you have 2000 sites, it will take too long to load.
So the true limit is dependent on how long you are willing to wait for a customer to open.
Once you start to have dozens of sites, it is recommended it be made into a Master Account instead.