Some day I guess I have to get a box blade to find out what the hype is all about....
To the original list, I think I'd add:
Mower - Some flavor... You're going to have to keep those hay fields cut until you get them all converted over to veg. Plus there's always going to be grass somewhere... You can get a rotary/brush hog cheap. On the other hand, you can keep it all cut with a finish mower if you don't let it get out of control, and it'll be a nicer unit to run for whatever grass you keep as grass. We keep all our fields cut with a finish mower behind an 8N. Flail is another option, I just don't know how they work with the gear selection on an 8N/NAA.
Back Blade - We've got a 5' that has been good for our needs. Takes care of most of the snow plowing. I'd be looking for a 6' if I was starting from scratch so it covers the tread width when you put some angle on it.
Trailer - When we were doing a lot of veg, we were always needing a trailer to haul transplants to the field, irrigation stuff, veggies from the field, rotten veggies to the compost pile, etc... That got mostly supplanted when we got a Gator (and stopped with the veggies), but the dump trailer is still invaluable at other times.
Other than implements, you may want to keep an eye out for:
Wheel, and or axle weights - Don't forget weights on the front wheels. These tractors are kind light up front when you hang an implement out back. The weights that sit over the axle are great, and are out of the way. I'm assuming they would work on your machine, ours are on an 8N.
Tire Chains - Great in the snow/ice. Can be useful when field plowing (so I've read, we never used them for that).
Make sure you find out all the parts that work with the 3 pt hitch, and how to use them. Sway Bars, Stay Bars, Draw Bar, and Top Link. You're likely going to need them all at some point.
Congrats on the tractor. There are obviously lots more advanced machines out there, but the N series can do an insane amount of work, and are easy to maintain. Once you get going, they're cheap enough that you can get another if you don't feel like taking a particular implement off all the time... We picked up a second 8N just for mowing.
