Digital Lowpass Filters, basic questions
If you want as little delay as possible, I recommend notch filters at your resonance frequencies. If your resonance frequencies are fixed, it should be easy. Otherwise, a low-pass filter at about 100 Hz should do the trick.
No your delay depends mostly on the cut-off frequency, the order of the filter and the filter type. An order-2 IIR filter will have a smaller delay than a 30-tap FIR filter . Your sample rate will not affect (or barely) the delay.
Typically, the lower the cut-off frequency, the higher the delay and vice versa. Also, an order-2 low-pass IIR will typically have a smaller delay than an order-4 low-pass IIR for the same cut-off frequency. 
If you can live with non-constant group delay, an IIR should do the trick.
Yes it does, but it assumes that you know what your resonance frequency is. You can maybe adapt your notch filter to the resonance frequency in real-time.. it is feasible but can be a lot of work.