I'd say she looks good..nothing there to worry about..
You should see them after 6000 hours...
1) Way less that would be expected..just get the big stuff if it makes you feel better.
2) If the Linear rails are wet then you should be good to go..I doubt that 226 hrs any of them are plugged..unless somebody used really poor way oil..unlikely
5) Both..if the gasket is good I use a gasket sealant..or just RTV..or both
6) Not necessary but really no reason to remove them..might just make it a point to clean under then as a normal thing..