The first thing you should do is write the list of things he must do and have your boat, that is, everything that serves to define it perfectly. Immediately afterwards, draw a general arrangement, even if it is very schematic, to check, among other things, that there is enough space on the boat for everything that must be carried on board.
Regarding the software, there are many on the market, some of them free but since your boat is quite complicated, I don't think they will be of much use to you. Maxsurf is a very good program, but quite expensive. If you speak Spanish, I can offer you my software, ARQN, which works together with AutoCAD. In addition to speaking Spanish, you should have an AutoCAD license.
At the moment I don't think I can tell you anything else, until I know more details about your project.