I am a new user and have already setup my phantom 3 to work with my iPhone. I purchased a larger clamp and want to know if I can also link it to an ipad mini. if yes will I have to update the firmware again?

If it works with your iPhone it should also work with the ipad Mini (depending on which generation, older iPads Mini might not work) No firmware update should be needed.

Agree with 2#. IPad Mini 2 or later versions are suggested.

I've been using an iPhone 6.  Just put a bigger clamp on and started using an iPad Air 2.  No problems, plug and play...