Which account I should use for defining “Service Account” for SharePoint products and sql server reporting

I have installed the following:-

1. SharePoint server 2013.
2. Visual studio professional 2012
3. Sql server 2008 r2 sp2

And currently I am installing visual studio team foundation server 2012, but during the installation I was asked to provide an account name to be used as a service account for SharePoint products, so I have the following questions:-

1. Should this user already exists?.
2. I have already define a service account while installing the sql server, so should/can I use this account?

Thnak