I'm so sorry for your diagnosis. I take it your legs are affected; go to the Motor Vehicle in CA and pick up a form for handicap parking, which your primary care doc can sign--be sure and check the maximum length of time--otherwise you have to renew every 6 mos.
Search the web for the ALSA of California, find on it a toll free number to call, and you will find them very helpful--to the extent of probably finding loan closet items including a power chair. The coordinator assigned to your area will likely do a house visit, which is also helpful. That person is the one who you will be emailing and calling for many things, most likely. Also, find your MDA assiciation--we're "Jerry's Kids", and with a Neuro's signature, they may also be helpful--they provide differently from the ALSA, so be sure and contact both.
People do their legal work at different times. Visiting and reading here at the forum, which I assume you've begun doing, means you'll read about the various on-set issues, you know everyone's progression is very different from another's, and you will or have already read about the PEG for feeding, the Bipap for breathing helps, and also about Venting as a possibility. I have not been following the "Do I Have" section and don't know what you've already shared, but you can download your state's forms for Advanced Directives, as well as for DNR if you so choose. My husband is automatically my Power of Attorney, so I know nothing about that--unless someone else answers your question on that, I recommend a search (see the search above in the blue bar?) The word is in white--or do an internet search.
The ALSA has materials to read online, and also in booklet form which was brought to me. These books hold answers to many basic questions.
Very best wishes to you. I hope your period of shock isn't terribly long or deep. I will now search for your previous posts.
Ann