GNU Radio loop bandwidth normalization
I can only answer your second question:

"How can the loop bandwidth in GNU Radio synchronization be configured as a percentage of the symbol rate?"

The tracking loop in the symbol synchronizer block operates at the symbol rate, estimating timing error and making a correction once per symbol.  So the sample rate of the error signal from the TED is at approximately 1 sample/symbol.  (I say approximately, because technically the block is continually estimating symbol clock error and adjusting its estimate of the symbol clock period, but its objective, nominal operating rate is 1 error sample/symbol.)

This means that in terms of normalized digital radian frequency, $\omega T_s$, for the loop filter, the symbol frequency corresponds to $2\pi$ radians/symbol.

The loop bandwidth parameter of the symbol synchronizer block is expected in units of the normalized digital radian frequency.  So when one specifies $\dfrac{2\pi}{200}$ for $\omega_n T_s$, one is specifying an approximate one-sided loop filter bandwidth of $2\pi \cdot 0.5\%$ radians/symbol, a one-sided filter bandwidth that is $0.5\%$ of the symbol frequency.

To express the loop bandwidth input of the symbol synchronizer block as a percentage of the symbol frequency, just use

$$\mbox{(one-sided) loop bandwidth} = \omega_n T_s = 2\pi \cdot n\%$$