Carl,
You are getting good advice and I'll throw in my ditto'as well.
Beside the FEL I have a box blade, a rotary cutter and a backhoe. The box blade and backhoe are the primary implements hanging off the 3PH. The box blade I have is Dirt Dog brand out of GA and to throw it in a catagory its a medium duty implement. It's built tuff but it was cheaper than other brands but not to cheap. It does the job so far.
Since you can push backwards as well as pull forwards with a box blade it might be a more usefull implement than the blade. But the box blade and the blade have the good points and bad but I figured for me the box blade was the way to go.
Another thing to consider is to use a hydraulic top link for your 3PH. I would assume it would be usefull for a blade. I KNOW it is a real must have for a box blade. You can adjust your boxblade without leaving the seat and while you are moving stuff around. Its a MUST have.
Also consider a 4n1 bucket for the FEL. You will have to be carefull with this because of the extra wieght of the bucket . The 4n1 bucket might take a good percentage of the lift out of your FEL on a smaller tractor. HOWEVER, the 4n1 is one of my most used implements. I was telling someone this weekend that without the 4n1 I think I would be only getting 50% of the capability out of the tractor. If you have anything to grab like wood, rocks, brush, etc., the 4n1 is the answer. The 4n1 can also be opened all the way so you have a "dozer" blade on the FEL. I use the "dozer" function to push stuff all the time.
However, if you do want a 4n1 bucket and a hydraulic toplink you will have to get the third SCV for the tractor and some other plumbing.
But again it really depends on what you are going to use the tractor. If you don't need to pick stuff up or push things often then you might not want the 4n1. If you have a gravel driveway to maintain then a box blade or blade is a usefull tool.
Ask the dealer about the new latch for the front of the JD FEL. I have a JD 4700 with a 460 4n1 FEL. JD is supplying, maybe after the purchase, a latch the holds the FEL L plate(my name for the gizmo) onto the front weight bumper. I'm assuming the FEL you are looking at works the same as the 460. The 460 has a L shaped piece of metal that locks over the front wieght bumper. There is a lever on the left side of the FEL that is used by the tractor operator to open and close the L shaped bracket over the wieght bumper. It is used to remove/attach the FEL to the tractor. The new latch fits over both the wieght bumper AND the L shapped bracket locking the two togther.
It really is easy to see and use but far harder to discribe.

Just make sure they give you the latch. Even without the latch if everything is adjust the FEL is really secured on the wieght bumper. The latch just makes sure it ain't going anywhere.
The JD FEL is VERY easy to take off and and put back on.
Hope this helps...
Dan McCarty