Can a F1 student in USA who is on OPT work on W2 (full-time) and also work as a freelancer (sub-contractor) and give invoices?


New Member
I am currently on F1 visa on OPT. I am currently working as a full-time (40 hours) employee (not a consultant). I am on company's direct W2. I have got another opportunity to work as a part-time sub-contractor (about 12-15 hours per week) in my field of education (STEM). The part-time employer said that I would be working as a sub-contractor and would be sending invoices of my work done and would get paid.
I have asked my DSO that if I could work for two employers and she agreed that I can if it is in my field of education.
The questions that I have:
1) Is it okay to work two jobs, one on W2 and other as a sub-contractor?
2) Will I have any problems in doing H1?
3) How should I invoice the 2nd employer (any recommended software)?
4) How should I file taxes and which forms to fill for taxes?

A detailed help is really appreciated.

Thanks in advance.