Good writeup! I love having my instagram feed in my reader. I did it the same way.
On your caveats:
- I manage to automatically syndicate stuff to instagram , but it uses their unofficial api and could die at any time.
- I think you discovered that you can only have once instagram cookie per browser at a time, so whenever that expires / changes is when the session is expired and you need to update granary. I don't know how long it lasts, but if you never touch instagram in the browser it is quite a while.
I can also highly recommend doing something similar for twitter via granary if you don't already have that set up.
In the future I hope to integrate granary into together in someway to make it trivial to follow public instagram and twitter accounts :)