I can only tell you my approach when I went through the same thing a year and a half ago. Sailing boats my whole life. Twin diesel trawler? Had never been on one. First, I read everything I could get my hands on for about 1 year prior to purchase. I think I read most of this site as well as grandbanksowners.com (not really true but you get my point) as well as a good bit of boatdiesel.com. Most of what I read I didn't understand but as I went along I became more knowledgeable on the conventional wisdom of many subjects.
When I finally purchased a boat I hired a well known local Captain and trainer to help me bring it north. A 1 1/2 day trip. Then I paid him to come back and spend a day going through the systems basics as well as 1/2 day on the water with handling. He gave me some pointers on how to practice on my own which I did for a few days after I got up the nerve to take it out on my own with wifey on board. Then I took one of his boat maintenance classes, two days and finally the Nigel Calder / Steve Zimmerman Diesel Engine course at Trawlerfest. That's the grand total of "formal" training.
In-between all of these I just went out on nice days, practiced slowing, accelerating, spinning on a dime, backing up, backing up and turning, played maneuvers around a buoy, etc. just to get more and more familiar with how the boat acts. Did so on smooth open waters with no one around. Found an empty dock are at my marina and practiced putting it in a wide open slip and against the dock with no other boats around. In short time I got to "adequate" on the handling scale. Wasn't that hard after a little practice and time. One final exam was putting it in between two boats to get fuel. It went fine and if nothing else my wife was impressed.
That's my story. Good luck with yours. My advice is to spend a few $$$ on someone who can show you the basics for a day or 2 and get you going. Go from there.