You don't need to use the companies but they are becoming more powerful. You will be added to the QME panel and get cases that way. Due to the increasing frequency of psychological problems, and changing nature of work (i.e. less manual labor), psych claims are much more common than in the past. The number of QMEs continues to decline (though there are quite a lot of psychologists). The rates went up substantially a few years ago. The QME mills (called "aggregators") are registered at multiple locations so they are more likely to get the cases but you still have a good chance of getting assigned cases without them. They handle billing, admin, record collection, scheduling, malpractice coverage, office space, training, dictation and transcription. some will pay for training and the QME certification. Thus for some people it may be advantageous to use a QME mill but it is not required (though probably is becoming more difficult to do this on your own).
There are no "intakes." You are doing a QME examination which a particular type of IME. You should probably be spending 3-4 hours+ evaluating them, less than 2 hrs would certainly be circumspect in most cases and then there is the time for record review and report preparation. Your report should also summarize records reviewed and relied upon. There may be a lot of records to review (it works out at about $300/hr for record review after the first 2 hrs which are included in the flat fee for the eval). Most people are doing some sort of psychological testing or at least malingering assessment (PVT/SVT) as part of these assessments and if they aren't, then they should be. Psychiatrists tend to be less familiar with these unless they have forensic training (and even then many forensic psychiatrists were not trained on this). The evals can be done remotely if you attest than an in person exam is not necessary.
Some cons to think about is that it can be depressing doing this kind of work. It is not as well compensated as doing other kinds of personal injury cases. While most claimants are genuine, there are high rates of malingering of some kind (exaggeration, false imputation, partial malingering), or unconscious exaggeration, misattribution etc that are not malingering but still relevant to the claim. People get upset if called out, or your opinions are not favorable to their case, which can lead to false complaints to the DIR or medical board or negative online reviews (QMEs frequently have 1 star reviews only by disgruntled claimants). Some people may worry about risk of violence, though you are more likely to be assaulted by a patient and both are relative uncommon events. The other issue if that the worker's compensation insurance is supposed to pay you for the work. There is no real enforcement of this so you could have difficulty recovering your money. They might also pay out less than what you billed in the way insurance companies make up their own rates. The DIR does not enforce their own fee schedule.
I don't do this work so don't DM me about it.