What are the key points to consider while designing the feedback section of mid power flyback converter?

Be sure to have a redundant Over Voltage Protection circuit. Feedback circuits can fail, allowing the PWM controller to attempt driving maximum output.

whats the exact mode of operation? too broad a question to answer precisely

Exact mode of operation is flyback as mentioned in the query.

Thanks Randy. I guess, the nyquist criterion can be also be considered while designing the feedback loop. Is there any other point which can be considered.

Well, maybe I'm too demanding, but just wanted to know whether the operation is PWM/PFM/DCM/CCM PSR or secondary feedback operated. Problems and points are unique to each.

Alright. I get your requirement now. Actually, my question was more generic in nature, that might be the reason why I could not understand your query. Let me say, that I would use a PWM operation with a secondary feedback using an IC like NCS
I hope this helps. Let me know if you need any more information.

Isolation of Primary and Secondary for feedback sensing of Output: Opto-Coupler, Third winding, Direct sensing through primary side waveform (i.e. LT3573)
What are your power/load requirements?

7.5 Watt LEDs as load

if the load is led, presuming constant current control, take good care in designing the loop bias of the opto. If you are comfortable with pole-zero analysis, apply the same to get a good staring point for the bias network. Too sluggish a response and you might just see things going haywire in short and open circuit tests later on. Using opamps result in excellent control, but such low power doesn't warrant the extra expense. Also, since you shall be using secondary side feedback, inconsistencies in primary current loop may not become apparent immediately, so look for inconsistencies in the circuit with your initial calculations.