Chosing the right motor for a vibration platform
How much weight you want to rotate is in itself irrelevant. What you need to know is two things:


what is the vibrating mass, vibration frequency and how fast you need to change it
what amplitude of vibrations you need
how much energy you expect your "harvester" to absorb


Vibration amplitude will give you an estimation of torque. For example, a vibration plane of 100 kg vibrating at ±1 cm amplitude will produce a force \$F=mr(\frac{2\pi}T)^2≈40N\$. That force has to be countered by your rotating weight, e.g. 1 kg weight attached to a 1 m arm. That weight would have the moment of inertia \$I=mr^2\$, and you will need a torque \$\tau=\frac{2\pi I}{T*T_x}≈6.28 N*m\$ to get it rotating at \$\frac1T\$ frequency in \$T_x\$ time (assuming \$T=T_x=1\space s\$).

The power of your motor will need to allow that torque to be applied up to 1 RPM plus cover whatever power you expect your harvested to absorb: \$P=\frac{\tau*RPM}{9.5488}+P_{harv}\space(kW)\$, which is 0.66kW + \$P_{harv}\$ in my example.

Hope that helps somehow.