How do I withdraw work authorization under TPS and apply for new one under OPT ?

DSO can smoothen the process for you.

Where should I send my opt out request?

Direct your request to the NVC. Good luck.

You need to have the principal visa first. Contact them. it happens sometimes.

For filing GC under EB1 category, does H1 status require to change to L1 ? And How much time it takes?

There is no legal affiliation between the two types. Now that you have changed, if will not hurt either.

Can I enroll for summer courses while I am waiting for a change in status from H1b to H4

I agree with my colleagues. You should be fine.

Can I start a company in US on F-1 visa?

You know that there are restrictions while on F1 visa. Your international office can guide you.

What is the best way for me to get an USA citizenship?

This is a serious violation. You will be banned from any immigration benefits in the future if you marry merely for obtaining LPR status.

First, your question is not immigration related. However, if you want to become green card holder afterward, you need to consult with an...

Will my approved TPS status still be valid if I travel abroad with my AP based on pending I-485 when I come back as a parolee?

I agree with attorney Alexander. It is probably not a good time to leave US.

Should I write Unknown in the blank fields if questions or sections are completely not applicable ?

Unknown is not an appropriate answer. N/A is the right answer if not applicable to you. As my colleagues said, consult with an attorney.