must have input devices

I think the omni directional threadmills will give more motionsickness in titles that dont have native support. If they only emulates WASD there is no way that your in game movement will be connected to your bodily experience.

For detailed hand and bodytracking I think Perception Neuron would be interesting. I say this cause you already ordered STEM. The makers of STEM and the makers of Perception Neuron have a meeting next month about common software and hardware ecosystem (as I understand it). But hold of on ordering for a while. It might result in specially designed imu-gloves that works together with stems for calibration and positional tracking, or something else on the hardware side, so wait for a update.
Perception Neuron seem to come with some cool demos also.

I have perception neuron now, have whole body... but had time to get right arm working. Willing to collaborate with people, there is certainly a lack of vr to do that works with perception neuron at this time.