I would get one wide enough to cut out your wheel tracks, when at an angle. And some would depend on you'll mostly be grading. Driveway maintenance etc. I'd think a 7' would fill the bill, and yet still not be too much blade for the tractor. I suppose in certain situations, a 6' would stop it in it's tracks. But, common sense goes a long way when using something like that.
As far as the hoe. No doubt they are pretty darn handy. Got a Case 480C TLB myself. But, if that is the only tractor you have, just wondering if that convenience is worth tying up the tractor, especially if you rigid mount it.
I'm just thinking for the cost of that hoe, it would go a long way on rental hours for a mini excavator. Let the rental machine take the beating, and save your tractor. Not sure what all kinds of projects you have in mind, but say putting in tile, and covering with gravel. IF you would happen to have a buddy help, one could dig with the hoe, and the other true up the ditch, install the pipe, and be covering in gravel, while the hoe keeps digging. Or even just a French drain, one dig, the other true up the ditch, and be placing gravel.
With a 3 PH unit, digging stumps etc. as mentioned will work on the 3 pt. arms of the tractor, and possibly even more.
If that was my one, and only tractor I depended on for all of the chores, I'd probably go with a rental unit, and save my tractor for the daily/weekly chores.