I've got a TomTom Rider 2, but can't speak for the Rider 1.
where have you fitted it
Under the seat, in the storage compartment between the toolkit and the battery. Loads of space. PMR radio fits there, too.
Can one of the bluetooth reciever adaptors be used on it to get Bluetooth from my tomtom to my autocom headset, I don't have a headphone outlet on my tomtom power connector
Yes, you pair the TomTom to the Autocom dongle instead of your phone, if you use it. If you still want to use your phone, pair that with your TomTom.
The genuine TomTom cradles don't have audio output, either. Design flaw IMO.