I'm sure an electronic controlled throttle, throttle body from a newer vehicle could be setup to be twist, lever, just about anything controlled, I believe you could actually use an LSx throttle body for this, and the hardware should easily be available for it to be standalone, as the pedal stuff is commonly used in retrofit applications using LSx engines.

As far as the automatic, while Im not sure if the powerfc may be able to do what you've listed, I do know you can take care of this using a 4L60E and stanalone transmission controller, there are aftermarket standalone TCU's for the 4L60/4L80E transmissions that allow tapshift setups in aftermarket installations, using one of these would allow you pushbutton upshifts/downshifts. You shouldnt have much trouble finding an adapter setup to generally use a TH350/TH400 or powerglide behind virtually any engine you could choose, and the bellhousing flange is the same for the electronic controlled transmissions just the same.

Hopefully this helps with your plans.