You are asking good questions. MSRP on the mid-PTO kit is $525. If you go with the rear-mount, you'll never need it. Ground clearance might not be listed since each tractor has three different tire options and all are different heights. I'd say roughly 2 inches. The shuttles are durable, but if you mow a lot, especially precise mowing, you will appreciate the fact that an HST by nature has ground travel and PTO independent of each other. The PTO spins away regardless if you are going forward, backward or stopped. On the Max28XL shuttle, if you push in the clutch to stop ground travel, your PTO winds down. That isn't the case with the 3016 and larger shuttles, but is the case for the 28. Tractors were that way for decades and we all got along fine, but having a PTO that is independent of travel really is better. In summary, go with the HST for your application.
I use a Max25 mostly at home. It does not lack for power. I do have to shift to low range for some things I do. I have a big drop-off that I fill with grass clippings and leaves and other yard debris. Sort of like a huge compost pile. It is soft, and the sides are steep. I generally have to go to low range when I am playing in that area. Otherwise all mowing is done in high. When the Max25's first came out I mowed my 10 acres of pistachios with my 6' flail mower and it did great. I'd generally recommend a 5', but the 6 footer never even thought of bogging the engine down. I do mow often though, so I wasn't mowing tall thick grass.
It is easy to keep stepping up in size. The Max22 would work fine for you, but the Max25 isn't much more and has a larger engine. From that point, the Max28 is a little heavier and lifts more and has larger tires and isn't that much more. But then the 3016 is a real step up in size...and isn't that much more. Soon enough I'll have you in a mPower 85 with a cab...for not that much more. So figure what you need, and try to keep your focus and do not step up in size needlessly. Just my thoughts.