Welcome to the forum. There are people on here far more qualified than I to answer questions on the "Dickie". There have been several good build logs on its upgrades. However, to get you started on answering some of your questions:
ESC: this an Electronic Speed Controller. As it says, it controls the speed and direction of your vessel. They are firstly rated in amps and sized to match the current draw of your boat's motor. In its selection one considers whether you are running a "go fast" boat or something more sedate, like a tug. The "go fast" controllers don't usually have the fine controller at the lower speed ends you would want in tug, for example.
There is an excellent introduction to the needs of boat electrics on the home page of this site. On the home page, look at the yellow bar on the left of the page. On the list is "Technical Stuff". Open this and you'll find a heading "Electrics". Go into this page and you'll find a lot of information to get you started.
In the main search are you can put in "Dickie" and come up with a number of builds and modifications to the tug, one such is at:
http://www.modelboatmayhem.co.uk/forum/index.php?topic=14677.0 Good luck with your vessel and welcome aboard.
John