Hey katherinebee,
Thanks for the question and congratulations on your new iPhone 6. I understand that you have a few questions pertaining to Photos in iOS 8, and I hope the following information proves to be helpful.
iCloud Photo Stream store your last 1,000 photos or photos from the last 30 days:
Where can I find the My Photo Stream album?
In iOS 8, there's no longer a separate My Photo Stream album. Instead, photos that were in the My Photo Stream album are now in the Recently Added album.
My Photo Stream stores your last 30 days or 1,000 photos. My Photo Stream keeps up to 1,000 of your latest photos updated across your iPhone, iPad, iPod touch, Mac, and PC. Photos are stored in iCloud for 30 days, and you can download them to your devices during that time. The Recently Added album also shows videos from the last 30 days. Videos aren't uploaded to My Photo Stream and won't update across your devices.
via Get help finding your Photos in iOS 8
If you have photos older than 30 days on your previous device, they may not be stored in iCloud anymore. You can import these photos to a computer, then sync them to your new iPhone:
iOS: Import personal photos and videos from iOS devices to your computer
http://support.apple.com/kb/HT4083
iTunes: Syncing photos
http://support.apple.com/kb/HT4236
Thanks,
Matt M.
