Absolutely no disrespect intended, but it sounds to me you're in over your head.
You'll need someone to come in and set pilings for the dock, that are deep enough to keep them stable. Be they concrete, wood or whatever, this isn't something you can do by hand... Depending on the company used and the area in question, they'll either bring in a truck or barge to do it...
Before any of that is even done, they BETTER get any necessary EPA approval and local permits etc. Sucks when you build something and someone complains/finds out then you have to tear it down and restore the 'wetlands, etc' back to the way they were prior to your construction.
I'd suggest you find someone who's experienced in dock building and pick their brain... Also couldn't hurt to just go down to the building inspector's office and ask them what the proper procedure for such a thing would be...
If you DO take the job, go into that job with all the information you can.... I've seen a few knuckleheads lose many bucks after finding out they can't just do stuff on wetlands/coastline whenever and however they want to.
Not sure that was the sort of answer you were hoping for, but that's my advice as someone else in the building trades... Hope maybe it helps you some.