A UFO would be interesting, especially if you could abduct other players. However, It would need to be expensive.
more practically, a hovercraft would be somewhat cheaper. As far as horses, I hate the way that if you get hit by a monster, you get knocked off. It needs a vehicle that offers protection. Maybe instead of a hovercraft, a hoverboard like in back to the future.
For the watermill, its not decorative. It consists of two blocks, the "wheel" or hydropower block, and the grinder or hydromotor block. intermittent driveshaft blocks can also be used between the two. If placed adjacent, with the hydropower in water, and the hydromotor adjacent or connected by driveshaft blocks, then the motor does work. Maybe grinds grain into wheat, stone into gravel, diamond into diamond dust, gold into gold dust, iron into iron dust, etc. The dusts can be ground into finer dust, which can eventually be smelted into ingots.
I know! if you grind iron ore into iron dust, you can smelt that into steel!
Include the sieve in the process, to make it necessary to sive the dusts to remove impurities before smelting.