Can anyone suggest on how to start modeling of this component?

Here's how I would do it:
1. Start with the rectangular body in the center. Just do the outside, and ignore the inside for now
2. Add in the 3 round flanged bodies. Again, just the outside shapes.
3. Cut out the inside hollow areas. Both the Rectangular and the Round openings.
4. Lastly, put in the mounting holes

Layout the construction axis for each line then build the rectangular body as Jack suggests, this should help with the development of the model.