Can I recover all my iCloud and iPhone data post my iPhone theft?

If you copied data to iCloud, you will very likely to be able to recover that data. There are two ways that you could have copied data to iCloud:

• By synchronizing data through iCloud. (For instance, by enabling iCloud Photos on the first phone, before it was stolen.). If you synchronize another Apple device against the same iCloud account and the same data, that data will start showing up on the new device. You can also log into the https://www.icloud.com/ Web interface from a Mac, PC, Linux PC, ChromeBook, tablet, or smartphone to see what is there.
• By making iCloud backups. The only way you can see what is in these is to restore them, which will wipe out the existing contents of the device to which you restore them.

If your phone was connected to e-mail accounts where e-mail and calendars lived on the e-mail provider's servers – the usual arrangement – then reconnecting the e-mail accounts will get you access to your e-mails.

If there was data that existed only on your stolen phone, there is no way for you to recover it. E.g., if you were not using iCloud Photos, and were not making iCloud backups that included photos, and had not copied photos off of the stolen phone in any other way, the photos on it would be gone.