Mmmm...
.... Is there a maximum groundspeed for taxying?....
From the RFM ...<6400Kg G Wt Max Taxi speed 40 Kts BUT taxi above 20 Kts requires nose wheels lock to be 'locked'.
For A/C with 6400-6800kg gross wt max taxi speed (on paved sfc) 20 Kts. Taxi on grass prohibited.
... Is there an annunciator or audible warning for an exceedance of such a limit?...
Not that I know off.