M,
You did good. As I understand it, the main difference is the exhaust on the new ones has a catalyst built into it. Not a real good idea as diesels run cool, especially when unloaded. This requires a ton of high RPM operation periodically to keep clean. You don't have to worry about any of that stuff.
I have had my low-time used L3800 for over a year now and have put nearly 70 hours on it. Except for a niggling periodic problem with a safety switch that interferes with starting (too busy to troubleshoot), I have really enjoyed the power and capability of a larger tractor. My first tractor was a '74 Ford 2 cylinder with 21 hp.
The HST is awesome. My wife loves running the tractor because of it. That makes the tractor that much more useful to me as I have a ton of landscaping to do and she prefers I catch the 400lb boulders while she drives rather than vice versa. Wives... go
figure.
This website is chocked full of people with years of experience in both the use and maintenance of these orange creatures. Spend a few days wandering through the pages and you'll understand.
As for the 3800, if it is your first tractor, you'll wonder how you got along without it. I think of it like a Swiss Army knife. The loader is great for hauling material, be it dirt, rock, or boxes and stuff you are just trying to move from the house to the barn. There are a ton of implements you can get for the back that do all kinds of things. Sure makes life a lot easier.
If you have owned a tractor, you know all this already. Take good care of your new orange friend and it will return the favor.
Congrats!