I was in your shoes about three weeks or so ago. I currently have a craftsman II 18hp of about 1985 vintage. The frame and rear fenders are similar to yours and I think running gear is the same, 3 foward 1 reverse, 2 speed rear. Its an excellent rig, fairly easy to maintain and adjust when needed.
But I always wanted more. More capabilities, more versatility.
I started looking to replace old faithful, and walked into several tractor dealers. Due to sticker shock, and size of tractors I kinda chose the Kubotas, even before I knew this board existed. The BX series looked like they fit the bill. The first one I saw had the FEL and 60" MMM and was the greatest thing since sliced bread, HAD to have one. I did research on the web and found several good sites, but this one really stood out.
Do yourself a favor and read as much as you can in this forum as well as the others. Do use the search function, as it can cut down the time it takes to find answers to your questions. But don't be afraid to ask questions about your potential new tractor. I don't think I've seen a sarcastic reply to a question yet.
My money is semi tight, and after looking at financing options (there's an excellent thread in the kubota buying forum on this, BTW), and what I want to use this tractor for, I narrowed down my choice to a BX1800 with a 54" MMM, (taking delivery next week!) with the FEL to come later. Take a realistic look at your needs and what you want to use it for.
If you've never really dealt with anything larger than a garden tractor before, Yeah, its going to be a big culture shock. The BX really is close as you're going to get to a regular farming tractor, just in a little bigger than a garden tractor package. But its not something anyone here has not gone through before and they have lots of smarts on the subject.
The key is to read as much as you can on this board, and take a look at the in the pictures forum to see what you can do with your new machine. Oh, and don't forget to spend a lot of time over in the safety forum to get an idea of some of the dangerous aspects of tractoring. I found a few thing that I had never thought of before, that may be different from operating a garden tractor.
This board has a wealth of information, like a whole library on Kubotas to answer your questions. Good luck on your decision!
Doug