As a designer and builder as well as a marine electronics/electrical technician I have seen boats become in some instances large collections of electrical ‘things’ along with large battery banks to feed these electrical goodies. If you are building your own boat and it will have electrical equipment on board beyond the engine starter and maybe navigation lights, read on.
Depending on the size of the boat and what ‘things’ you want or need, having a professional help you or do the planning and installation might be a good idea BUT in my opinion there is a level of complexity an amateur can take on with the right knowledge and information that does not require going to school. What is this level of complexity? First keep your systems to a minimum. You will probably need navigation lights, maybe some cabin or utility lights. You may want a fishfinder or depth sounder, possibly a VHF radio, maybe a small chartplotter/GPS. You will need or should have at least one bilge pump, a horn, maybe a sound system. This is a reasonable list though not complete that could be handled by an amateur builder. What you don’t want to tackle for your first major project, dual 12/24 volt battery systems, lithium batteries and you might want to think seriously about having AC power stuff on board utilizing shorepower. AC power requires a lot of care. The advantage of doing the work yourself is twofold. First you save labor money and secondly and more importantly, you understand your electrical system and will be able to add to your system and repair your system, particularly if you are on the water.  I will be posting a procedure for planning your electrical project along with postings to develope the knowledge needed to be successful at doing your own project. After you build your boat, planning and installing your own electrical system is a real feather in your cap.