Is it possible to include an activation link in the Admin Approval email?

Not that I am aware, no.

Also, I need to include additional user registration information in the approval email. I would really appreciate any help/tips on where to start to do this.

New user registration email is configured through language strings. Please see CB language files; specifically the following.

IN: components/com_comprofiler/plugin/language/default_language/default_language.php
ON: Lines 164-177
[code:1]
DEFINE ('_UE_REG_ADMIN_PA_SUB','ACTION REQUIRED! New User Registration Pending Approval');
DEFINE ('_UE_REG_ADMIN_PA_MSG','A new user has registered at [SITEURL] and requires approval.\n'
.'This email contains their details\n\n'
.'Name - [NAME]\n'
.'E-mail - [EMAILADDRESS]\n'
.'Username - [USERNAME]\n\n\n'
.'Please do not respond to this message as it is automatically generated and is for informational purposes only.\n');
DEFINE ('_UE_REG_ADMIN_SUB','New User Registration');
DEFINE ('_UE_REG_ADMIN_MSG','A new user has registered at [SITEURL].\n'
.'This email contains their details\n\n'
.'Name - [NAME]\n'
.'E-mail - [EMAILADDRESS]\n'
.'Username - [USERNAME]\n\n\n'
.'Please do not respond to this message as it is automatically generated and is for information purposes only\n');
[/code:1]

The first subject and message is for new user registration and requires approval. Second is for new user registration but does not require approval.