Question about the detail necessary in the plans for the county can only be answered by the county. Typically they're concerned about the structural elements - dimensions and spacing of joists, footings, railing height, how it's tied to the house, etc. Is this deck going to be on grade or elevated from some point in the house that isn't shown in the picture? They're probably going to be less fussy about an at grade deck because collapse isn't an issue (although that drop off might be depending on how far the deck goes into the valley).

This is really a question the probably would be better asked in the "deck" section.

Talk to your inspector about what they want to see. All the ones I've worked with have been happy with a neat hand-drawn sketch. They are going to want to see details on footing sizes, all the structural members, rail attachment methods, details of how it attaches to the house if any load is supported by the house, and whatever else is on the inspector's hot button list that week.

Around here you won't get a permit to build anything within 100 ft of any running water, so you'd better check with your conservation commission, or whoever does that function in your town, as well.