Tough decision. No right answer. If you're like many of us, you'll put it off and hand wring a bit, and delay, and having carefully weighed all the pros and cons, simply do what you WANT to do rather than what might be smarter, as long as you think your objectives are achievable. Always boils down to risk versus reward, and if you really, really want to get on with it, you will.
My advice on the aux diesel is that you put as least as much effort into understanding how to operate it and do preventive maintenance as you do diagnosis and repair of failures. It's my gut feeling that engine abuse is responsible for the majority of issues.
Lots of resources available for you to learn to do both.
Go ahead and go. I wish I had taken my first long cruise in my twenties instead of in my fifties.
And, here is some more old age wisdom. There are very few financial calamities that can befall you in your twenties, (or even 30's) that you can't recover from. Not so much in your forties, fifties and sixties.
I took my first cruise to the Bahamas, on a 38 foot boat for two weeks, when I was in my twenties. Heading back home, I wanted nothing so much as I wanted to head that boat south and keep going. But, I had already saddled myself with a home, a mortgage, two new cars, and a wife, who wasn't nearly as shot in the butt with the cruising lifestyle as I found myself to be. It took 21 years after that before I got to do it. It was the single best thing I have ever done and I'm about to do it again.
If you can go now, and want to go now, go now. You have no idea what life may have in store for you in the future that will prevent you from going. Approaching 60, now, I wish I had done more of the things that I wanted to do back when I was younger (and, I did do plenty, I just wish I had done more), that I thought were irresponsible or not in keeping with society's and family's expectations.
You only get one lifetime and it's yours to live or not live.
What constantly amazes me are long time friends that say "Wow! I wish I would have done that." My question to them is usually "Then why don't you do it?" They all seem to come up with some lame excuse and never do IT.
Over the winters when I am not chartering in someplace warm I like watch sailing videos while on the exercise bike to carry me through these cold winter nights. I found a You Tube channel called Wicked Salty. It's a video log of a young guy heading south on his sailboat with his very attractive girl friend and a little rat/mop dog. I starting watching one of the later videos first when they were sailing in Long Island Sound on the boat just starting out last fall. At first I thought he was a little snarky and cocky. I'm also thinking how does this kid have the time and be able to afford to do this trip at such a young age. Is he a Trust Fund baby? Perhaps a successful Day Trader? Then I saw his first video: http://youtu.be/Nq8hOsO6FrA?list=LLgnzh-cPKnzc6-7yFsWlHbw
Seems the kid graduated college and worked his ass off all summer to be able to afford to buy a used boat and then set sail. Very inspiring and I am enjoying their adventures. Yeah, he is screwing up and getting into trouble (grounding) from time to time. As a lot of us have when first starting out. But, he seems to be moving in the right direction. He is definitely of the Just Go/ Do it now mindset. A good inspiration for those considering such a move IMO.