Can I subpoena him as a witness to my trial if he is very important to establish who my defendant is, his net worth?

Yes, you can subpoena anyone who has relevant evidence, but normally the wealth of the defendant cannot be mentioned at trial as it is only relevant if punitive damages are ought in the Complaint. If you think you have been damaged so much, you need to seriously consider hiring an attorney to at least give you advice. Your asking this rather fundamental question demonstrates you are not knowledgeable about the law. At the trial of the case, even if it is more informal because it is before a judge and not a jury, the defense attorney will object to any evidence that is helpful to you, will file a motion in liminie to limit what you can present, and will cite cases and legal theories to get your case thrown out. Some attorneys might be willing to handle it on a contingency fee basis [they get a percentage-normally 40% if it goes to trial] where they get paid only if you win. Most will not handle a case if a trial is coming up in a few months because they will fear that you will not follow their direction and you will sue them for malpractice.You have to balance the cost of attorney fees against the fairly great likelihood your case gets tossed out. You definitely must spend some money to get an attorney to look over your case and see what you need to do.