73 914 20 total rebuild, head and cylinder sleeve Options

[Brasil914]

good midnight all. so several years ago I posted about a high idle issue and that I had checked everything I could and couldn't pin point it well fast forward to this year and I decided to drop the engine and rebuild it. I'm very sad and need some input. So back in 09 when I acquired my 914 from my dad it had set since 86 because a spark plug had broken off in it. I pulled the head and got to looking at th cylinder to make sure no particles were in the cylinder. when I reinstalled the head I did not se that the seal ring was not properly set and it was wedged when everything got tightened down. so I need advice on the following pictures.
1. due to the slight depression from the ring I am thinking I need to have the seat honed I shouldn't need to replace the head correct?
2. what would be the best way to clean these hard deposits on the exhaust valves?
3. all of the sleeves look good but have noticed some deposits on the Piston. Do you think I need to replace the rings?
4. as you can see I had another spark plug break how common of an issue is this?

Dave Darling was a great help and I haven't really looked to see if he is still on here.