Never been up there before. Any advice? Anything else I need to do when I'm up there?
My advice - for what it's worth - would be to take as much time as you can on-site... so make sure you've waterproofs that can stand up to a prolonged Lewis downpour!
The satellite rings would all be worth long trips in themselves anywhere else.
Would also recommend:
1) Airigh nam Bidearan stone row
2) Dun Carloway
3) Clach an Trushal
4) Steinacleit