Hello. You will probably hear all about how the YM2000 and its US market twin, the YM240, are excellent tractors. They are. They are simple to work on and parts availability is excellent. There are several high-quality dealers who frequent this board and offer anything you would need.
This tractor should handle a 4 foot cutter and box blade fine. Your results may vary according to the tires the tractor has, the terrain/geography of your area, and so on.
I see you are also asking about a Ford 1900, and own a Mitsubishi D1620 or D1650. A search of the Yanmar forum will reveal many, many reviews and recommendations on implements and their usage for the YM2000/YM240. It is likely the same with the Ford 1900. What's the purpose for buying another tractor to supplement your Mitsubishi? Will it not handle the implements you have? The Ford 1900 is significantly bigger and more capable than the YM2000. Here are some comparisons:
TractorData.com Ford 1900 tractor information
TractorData.com Yanmar YM2000 tractor information
These are the Nebraska tractor test data for both of the tractors you have asked about: (The Yanmar is the YM240, but it is identical in the important and salient aspects to the YM2000)
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2570&context=tractormuseumlit
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2695&context=tractormuseumlit
The Ford will be significantly more capable, because it is much heavier than the YM2000. That isn't necessarily an advantage. Larger, heavier tractors will, all else being equal, tear up the ground more than a smaller tractor will. It doesn't take much of an increase in platform size to make a tractor more awkward in tight spaces. This may or may not be a concern to you. If you brush hog large, open fields, the Ford may be a better choice. Sell your 4 foot cutter and size up. A 5 foot cutter will, under ideal conditions, be 25% faster.
Search in each forum for the keywords of the tractor you're interested in. Read a bit, see what shows up. I'm new here too, but this website is an excellent resource. If you use it efficiently, you will be a lot happier with the results.
And again, assess your needs. Why won't your current equipment do the job? Good luck!