Thank you all for your reply, suggestions and tips.
I have changed my plan. I am driving to Coorg tomorrow (Apr-27th) and coming back on 1st-May.
Will plan for Nandhi hills few months latter. I hope coorg is easy to drive for a new driver like me than Nandhi hills.
Good way to start. You wont find any problem in Coorg (Madikeri roads) unless you take any deviation to some jungle resorts.
Bangalore to Srirangapatna is with median and you need not worry much.
Be careful about:
Humps near mandya - There are lots of humps when you reach Mandya.
Vehicle coming towards you in one way. Lots of Bullock carts and even two-wheelers / four wheelers. If you are able to maintain good speed, i suggest you to ride on the right most lane.
From Srirangapatna to Hunsur road (towards Kushal nagar), you may find some patchy roads. Less than 8 km.
Follow the traffic rules. Make sure you signal while you turn / overtaking.
Ride safe. Even if you reach an hour or two late, be safe.
Happy Journey. Have a wonderful time.