请教F1 STEM OPT 如何cos H4

大家好，帮朋友问一个STEM OPT cos H4的问题，朋友是发我的英文，所以我就全部贴上了，谢谢啦。
Hi,
I am considering STEM OPT cos to H4. My spouse just recently got the 140 approved, and my STEM OPT will expire in 2021 May, which means I only have one last chance of my own H1B lottery. so I am thinking about if I need to cos to H4 with the future effective start date as the expiration date of my current STEM OPT.

1. If I submit H4 and H4 EAD application now and put the future effective date as 2021 May, is this ok? am I allowed to put the future effective date even more than 6 months from now?

2. If submit the COS now, does that mean my STEM OPT EAD will expire immediately? or it will still be good to use until the future effective start date of H4?

3. If Trump decides to cancel H4 EAD at the end of 2020, will this revoke the approved H4 EAD with a future effective date?

4. Let’s assume I can keep my current STEM OPT EAD until 2021 May and I am lucky to get my H1B picked in the lottery in 2021 April. Since I put H4s future effective start date as 2021 May, will this affect my potential H1B application? If not, do I need to submit H1B application after 2021 May (when I am in H4 status) and submit H4 cos H1B then? and in this case, does that mean I still can use H4 EAD between May and Sept. 30, 2021, and start to use H1B after Oct. 1, 2021 (assumed H1B will be smoothly approved in 2021)?

Thanks for your help with my questions.

Hope you stay safe during COVID-19.