Aloha and welcome aboard!
I was going to say that a good diesel engine
is the most expensive addition to a boat but someone already beat me to it.
There is a book title mentioned after my signature and a couple of links that you might be interested in trying. The search engine
linked there is a google
search that might help you answer specific questions.
Even if you are extremely handy in all things there are some boats that you should avoid so before taking the plunge post here in one of the other threads which boat you are about ready to put money
into and you'll hear from others on the forum who either have owned the boat or who have had experinces aboard them.
Good luck in your search. The searching part can be a whole lot of fun and if I were to do it again I'd buy a boat in sailing condition that just needs some updates and cleaning
up and a small repair or two. I've spent way too long rebuilding a boat and I'd rather be sailing.
is the preferred auxiliary engine.