If you already have a case number then you do need to file and serve the MC-050 on opposing party. To answer your question about the limited scope representation follow this link: http://www.courtinfo.ca.gov/forms/fillable/fl950.pdf
This is the form for Notice of Limited Scope of Representation. Your attorney should be familiar with these forms and able to take care of it for you.
Normally, your attorney would file a Notice of Appearance on your behalf. A subsitution of counsel would be where you already had an attorney and a new one takes his or her place. Whether your new attorney files a formal Notice of Appearance or not depends on how limited the scope of representation is agreed upon.
The answer to your first question depends on what papers you've already filed with the court. If you've filed nothing, then your attorney's filing of a first paper would make him your attorney of record.
This is for the attorney, not you, to take care of.
You would need to serve your spouse. I handle cases on a limited scope basis. I would be more than happy to talk with you. I charge reasonable fees. When parties are close to settlement, legal advice can help parties get past the impasse.
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