Excatly in the same boat. Leaving ios. So far enjoying it. Not played around too much yet with the camera. Is it and can we installed Google camera software on a p30?
I've not ported across my photos, videos and documents from iCloud, they are still in there and I was planning just to access all that from my desktop when required. I downloaded Google Drive for iOS and backed everything else up to a Google Drive then accessed that on the new phone to restore contacts etc. The biggest hassles were backing up SMS texts and WhatsApp chats, some of those I really didn't want to lose. The WhatsApp I *think* I have sussed out and backed up but because I chopped and changed back and forth between my old iPhone and new P30 with verification of numbers within the WhatsApp application itself, I've been locked out for 8 hours before they will re-send a verfication code. I'll know if its all worked later when I get the new code sent.
The SMS thing was a royal pain. There was a small program called iSMS2Droid which did it in minutes but its been taken down off the Google Play Store (there's an explanation online about why) so I ended up having to faff around with converting the backup of the chat archive from my last iPhone backup using DB Browser SQLite, then it started talking about having to drop that into an Excel spreadsheet, modify columns and stuff and I lost the will to live! So eventually someone I know suggested I download the latest iSMS2Droid apk from the web (they are still available - just make sure you grab it from a reputable source and check the MD5 Checksum matches the original), installed that and it worked perfectly. All SMS texts back on the phone.
Other than that it was fairly straightforward although I'm going to take some time to get used to the UI as its a big departure from iOS, but not necessarily in a bad way.