The detail of the report depends on the surveyor. In general, they go through most of the systems on your boat, do a sounding on the hull, and basically give you as the buyer their opinion on the vessel and what issues you might see. Values are ALWAYS subjective, but it is typically a fair appraisal if you use a good surveyor.
Now, that being said, let me warn you on a couple of things:
1) Not all surveyors are created equal. I cannot emphasize this enough. Get a really good, reputable surveyor.
2) Almost all standard surveys do not include the engine. A basic run-through, yes. But the indepth is not part of a surveyors typical routine. You will need to pay for an engine survey that will likely be more than the rest of the boat survey, in my experience (if it is a good one).
3) There are no guarantees. Just because you had the survey done, it does not mean that 5 seconds after you sign the papers, the whole thing won't fall to pieces. Gweedo might be a solution for revenge, but I do not think there is a legal recourse... if I am not mistaken.
4) No, you typically do not have to get a survey on a new boat. I never have. You have warrantys through the manufacturer and distributer.
5) Yes, they charge by the foot with many having a minimum charge.
I am not a surveyor, but know a good one who is a very knowledgeable sailor. I have done a fair amount of sailing with him and would highly reccomend him, but he mostly works Florida & Texas. If you want to PM me, I can give you his name & number and if he cannot help you, maybe he can reccomend someone that can.
Hope that helps. Fair winds.