Large todo lists can cause stress indeed. But getting things out of your head by writing them down also releaves stress.

I keep my todo's in trello. You can label tasks, for instance by importance and give the ones that need it a deadline. Only they pop up in my mailbox at the time the deadline is near.

Works like a charm for me.
But sometimes I remove the tasks that arent relevant anymore too. You have to keep the list clean.