In my late 2011 I have a 250GB Samsung EVO 850 and I replaced the CD drive with the stock 500GB HDD. This setup works pretty well for me as I have OSX, my applications and LR catalogs on the SSD, and I have some internal storage available as well. I keep my main photo archives on external drives at home, but the 500GB of internal space allows me to store some files on the macbook as needed.
250GB for the SSD works for me as I'm not really storing large amounts of files on the SSD, and I've tweaked a few things like turning off local Time Machine backups. If you use local Time Machine backups, iCloud storage, have lots of apps, etc, you may want to go with a 500GB drive.
The biggest problem I have with my late 2011 macbook is there are no USB 3.0 ports and only one Thunderbolt port. I use a $200 thunderbolt dock to partially alleviate this limitation, so I have reasonably quick throughput to my large external drives.