I bought a ZD221 last year with the 48 inch deck for the same reason as you, tight spots that a 54 inch deck would not be able to fit. I've got several areas where I have to lift up the discharge chute in order to squeeze by. The deck only sticks out a couple inches past the rear tires on the left hand side, so you have to be careful when edging close to objects. I've already scraped the tire a couple times by accident. If you have trees with low hanging branches or shrubs you will probably have to hit those spots with a trim mower or string trimmer since the deck doesn't reach out far enough to let you ride by without getting hit in the face by the branches.
I would get the mower lift unless you already have something like a MowJack to raise the machine. It helps a lot with cleaning the deck and blade removal / installation. I like being able to drive up next to the hose, crank up the front of the mower in less than a minute, and spray off the grass that gets stuck on the bottom of the deck.
As for general machine comments, the engine and fuel economy is awesome. I rarely ever get RPM drop and when I do it's in thick clover. You will want hearing protection, although in my experience the Kubota is quieter than a similar size Kawasaki gas engine. The blades are an odd size, not sure if there are any aftermarket options yet. I just bought a replacement set at the dealer for $71 + tax. One of my front tires got a slow air leak shortly after purchase but I fixed that with slime. I actually did both front tires and both have held their PSI since last fall. The radiator screens collect quite a bit of grass in dry conditions, so you have to periodically stop and clean them off or else risk the engine temp climbing.
I wish Kubota had used swivel anti-scalp wheels on the 48 deck like they do the larger models. It's not a big problem, just would have been nice instead of fixed wheels. If you want to change the height of the fixed wheels you have to unbolt them and reinstall in a different hole. I always leave mine in the lowest position since I cut at 3 inches.
The worst thing about the Kubota, in my opinion, are the grease zerks on the shaft that goes from the engine to the transmission. You are supposed to grease these every 50 hours, and a couple of them are tough to reach. One of them has to be accessed from underneath the back of the machine where there is not much clearance. The ones on the mower deck shaft aren't too bad, I will rotate the blades by hand to get the U-joint into the right position to get to the zerk.
