I divide as little as possible. I am sooo lazy ............... I dig rhizomes away from the clump to share, rather than do a proper division. In my climate/soil/spacing I can get away with 5 years, sometimes 6. A lot depends on the vigor of the cultivar. Thornbird (TB) is my fastest increaser.

The advice given is: divide when bloom begins to dwindle. In perfect conditions this may be after 3 years? If you have planted one rhizome like I do, you will have more time than that ~ provided there is 2 feet+ between rhizomes. I have planted closer but cultivars get mixed up too quickly. I'm too warm for SDBs so don't know if they multiply more quickly than TBs or not.

As to removing GREEN fans (leaves) --- no. The outer leaves of a fan turn brown and dry up. They can no longer manufacture food so may be removed. I suspect in your zone (5b) the plants are beginning dormancy and the brown leaves can be left on over the winter or removed now. People who do it in the fall think it's helps reduce borer eggs being laid in the foliage. Others don't find this to be a factor.