Q. Is it mandatory to purchase insurance as well as to get rto registration from the dealer - Access 125?

No, for a new vehicle, it isn't mandatory to buy insurance from the dealer. However in some cases you can get a discount or haggle and get the dealer to put the first year in for free. I am not too sure about the RTO registration. I have heard of people collecting their vehicle without a registration number but never heard of them collecting without registering at the RTO at all. Mainly because the vehicle wouldn't be legal to drive out of the dealership. Another reason is because it will be more of a hassle to do it ourselves (get a flatbed to tow to RTO and doing the necessary paperwork etc.). They know the process and do it regularly, best to leave it to them.

We can take the insurance with other companies also. But we need to purchase insurance before taking the delivery of bike

Insurance is not compulsary but Rto registration will be there