Hold in mind that Photostream is not a permanent album. Photos that go into Photostream can dissappear due to both time limits and limits on the number of photos. Photostream does not restore itself from iCloud. If for some reason Photostream gets turned off on your device, then turned back on, only photos taken after it's been turned on will be added.
People have a tendancy to treat Photostream as a 'permanent' recent photos album. It's not. It was meant as a quick way to share recent photos between your devices.
That's all just a long way of saying don't trust your photos to Photostream. Use it if you want so you can easily cop[y photos from one device to another, but don't leave anything there as the sole copy.
If you want a permanent album that shows up on all your iOS devices (and don't want to use iCloud Photo Library), iCloud Photo Sharing is the way to do it. You have to add the photos to albums manually, but they are backed up in iCloud and will come back if the iOS device loses them during a restore, update, or other reason. I used ot use photo sharing a lot for just this kind of thing.
Note: iCloud Photo Library makes both Photostream and Photo Sharing redundant for personal use, but tends to require more space than the 5GB of iCloud storage Apple gives you for free.