1.Yes you can use AD and LDAP protocol. Sitefinity 4.0 you have to configure the AD provider from Sitefinity/Administration/Settings/Advanced and then go to Security >> LDAP Settings.
2. You can use several membership and roles provider. Can you explain some more about
"it possible to use Sitefinity’s Built-in / Custom Roles instead of Active Directory groups? If yes, please provide step by step instruction on how to achieve it also."
Here are some basics
You can use several membership and role providers from the front end ( public part ) and backned ( admin part).
Once you enable a second membership provider the backend login form control shows a drop down which you can use to switch the providers. Inside Users section in the administrations you will be able to see all users and providers.
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