H1-B filing suggestion please

My H1-B pre-registration from Employer-1 has been picked in the lottery this year. I was given time to file my H1-b petition within June 30 through employer-1. However, I don’t have a project with employer-1 currently. In the meantime, I received full-time offer from another employer-2 with start date in May first week. What are your suggestions for me to file my H1-B through employer-1?

Also, I am currently on OPT EAD. I am due to apply for STEM OPT extension by June 30, 2021. Should I apply for STEM OPT through employer-1 or employer-2? If I apply for STEM OPT through employer-2 and H1-B through employer-1, would there be any issue as both the applications are to be sent to USCIS? Please advice.