What is the purpose of having multiple workers on the website? Do I need one for each computer I have here at home mining or can multiple computers use the same worker account?
It's recommended to have each miner instance to be used with separate worker credentials, so you will see witch ones are working and which ones are not. Also you can compare their stats.
But if your setup doesn't allows you to use separate worker accounts, you can use up to 20 miners with Long Polling support on one worker account.