First time using an iPhone
Can the Google play store be downloaded on the iPhone with my Google
account?
Answer: No you can't download Play Store in any Apple device.
If not how do I download games &amp; apps &amp; what do I use to
do it?
Answer: You can't access your Google Play purchases, so you will need to use App Store to purchase/download again any app you want, iTunes app to purchase music, iBooks app to purchase books...
Do I have to have an iCloud account or iTunes account? 
Answer: You have an Apple Id and you will use that to log in into iTunes and iCloud, you have some 5GB free storage, if you want more you need to pay.
Can I use my Gmail/email account or do I need to have a Apple
email account?
Answer: You can download Gmail app from App Store, you don't need to use Apple accounts, although you get one when creating your Apple Id account.


Finally, you can easily get step by step tutorials for any of this topics if you search in Google like How to... setup iCloud Account, create an Apple Id, etc