How tall is the brush you'll be cutting? Is is mostly just taller grasses, or is it more brambly and smaller trees? Is the property level and flat?
Have you ever operated your 4210 and cutter without the loader installed before? How did the front end feel (if you have)?
My tractor, a Deere 790, is pretty close in power. Your 4210 weighs a couple hundred pounds more then my 790 (2400 vs. 2200...both numbers rounded up to the nearest 100 lbs).
I just cut the couple acres of field without the loader installed. This is the first time I've used the cutter without the loader installed. The front end got pretty light on some of the minor slopes I was working on. There's no way I could have raised the cutter in transport position without the loader or front weights. Frankly, the lightness of the front felt a bit uncomfortable.
So, yes, you can operate your tractor sans FEL. Just take your time so that front end doesn't bounce around too much. If you're going to do this on a regular basis, you'll probably want to get the front weight kit.
Now, a caveat...
Before you load your tractor/cutter on the trailer, try raising the cutter in transport. You may find the front of the tractor comes up off the ground. Raise the 3PH slowly, so if the front does come up, there won't be any surprises. Were you planning on driving forward up the trailer ramps, or backing up? Driving forward with the cutter in the raised position may result in your front end coming off the ramps (up, I mean).
So, even though you can operate the tractor/cutter; it might be very difficult to load or unload it on the trailer.
If it turns out you can't safely load (or unload) the tractor/cutter from your trailer, I suggest you install the FEL, drive forward up the ramps and lower the cutter so it overhangs the end of the trailer. My guess is the side skirts of the cutter will bear most of the weight. You could remove the cutter's tail wheel for the trip. Another thing to consider is the tongue weight of the trailer. With the cutter that far aft, I'd be a bit concerned about the weight distribution of the load. It's not that you'd have too much weight on the tongue, but not enough. Hitting a bump on the road could result in the trailer bouncing up off the hitch. Since your trip cannot be more then a few miles (you mentioned 45 minutes if you drove your tractor...that means around 7 or 8 miles) just going slow may be enough. I'm assuming your trailer has brakes and lights?
If you do what I've suggested, make sure you use tie-downs on the tractor and the front of the cutter. Don't depend on the 3PH holding the cutter down!
Of course, I'm not there, so I've got to base these comments on experience and semi-educated guesses. But I think these comments will give you things to consider. However, if the load does not look safe (too much of the cutter length hanging over the end of the trailer), it's probably best you make two trips as a previous post suggested.
"First I don't have plates for it and second it will about 45 minutes to get there"
You really need plates to operate your tractor on the road in MA?
