On the peripherals subject you do have a good reasoning there I reckon. I don't think there are Harmony controllers with keyboards, although you could program a keyboard on the touchscreen, character by character, but that would be cumbersome and not very effective, since text input is not an ideal thing to do over infrared.
As for the Harmonies, well most of them share the same awesome features, though some have regular AA batteries, some have rechargeable and a charging dock, more buttons, touchscreen or not, a smaller or larger screen, etc. The ONE is fantastic. It was released 2 years ago and it's still the top of the Harmony controllers that aren't crazy expensive with RF features, etc.
To set it up with a Mac mini is easy as pie. Logitech has a huuuuuuge online database of devices that you can automatically set up on your remote, and the Mac mini is obviously there. What is best is that even if you have a device that isn't on that database, your Harmony can actually learn any command from any controller, so it can pretty much control anything that has an IR port.
And the level of customization possible of all the actions, activities, macros, etc, is crazy. It is truly an open remote to anyone to program it to do whatever.
I say that even if you go for the kb/trackpad combo, which also has a lot of perks, in the long run consider an Harmony, even the cheapest one you find.
In fact, in the long run I also want some sort of wireless kb/m auxiliary, I'll keep on waiting for the fabled Apple wireless keyboard/magic trackpad all-in-one