That crank sprocket looks like it needs to be replaced to me. Your new chain will last about half as long as it should running that sprocket. You have to look closely for wear. See where the rollers have gotten into the right side of the teeth?
You can't tell how the tensioner is until you can see it.
Gasket? Clean and dry. Don't forget the donuts around the top two bolts. Don't gouge up your gasket surfaces cleaning off the crap that it never really needed. Man I have been seeing a lot of that lately! Permanently F'ed up stuff with no good cause for it.
Camshaft seal? That is the bean can's O-ring. Replace it. They are cheap.