Going downhill in b mode, gets fast quickly! Is this usual?

That's quite the slope if B doesn't slow you down.

Cruise control doesn't engage the friction brakes, just the regen braking from the motor. But cruise will not work in B.

 

What is significant about the 32 number ??

If the speed limit is 30, then you need to start down the hill at about 25 in B.......and/or let it go 35 and see if it won't level off about there.

But some manual braking likely will still be necessary.

 

How steep is the slope? What % grade?

No, cruise control (CC) won't use the brakes. But if the road is straight and even enough for CC, then go ahead and try it to hold speed steady. It will use the same battery regeneration and engine braking mechanisms that B mode uses, but applied in a bit different manner.

But if this doesn't hold back the car enough and you must still use the brake pedal, CC will disengage.