Activating an Apple Product

You will have the same apps if you decide to restore the phone's backup onto your iPad, they won't automatically download just by using the same account to activate it. You can use the same account, and have the same apps, on multiple devices.

The apps listed on this page will show as free for the account that you use to activate it : http://support.apple.com/kb/HT5913

Whatsapp is not available for iPads, the developers have so far only made a version that works on iPhones.

For emails you don't have to add your email accounts to the iPad's Mail app, so that shouldn't be an issue. Similarly for imessages, you can either not set it up on the iPad or create a separate account for use with it.

You can create a new account, but all of your existing purchases will be tied to your existing account, it's generally best to have just the one account (apart from anything else each account has to have unique email address(es), and you have to remember each account's password).

If you sign in with the same Apple ID, and do not restore from an iCloud backup, the applications you previously downloaded with the Apple ID will not automatically download onto the iPad. However, when using the iPad, if you or someone else opens up the App Store and go to the 'purchased' section, you could redownload the applications you previously had on your iPhone (assuming they also are compatible with the iPad). But, none of your data will be in those applications unless you sign in.