Advice on steps for applying for a parents GC

[HPP]

My spouse wants to apply for a GC for her mother who is 70+ and currently in the US on a B1.

As I understand the forms she needs to fill out are:
1. I-130, Petition for Alien relative 
2. I-485, Application to Register Permanent Residence or Adjust Status   
3. I-131, Application for Travel Document 
4. I-864, Affidavit of Support
5. I-693, Report of Immigration Medical Examination and Vaccination Record
6. I-785, Application for Employment Authorization

I had some clarifications on how to file the documents which I can't figure out from the USCIS website and I'm hoping folks who've filed for a GC for their parents could help me fill in the gaps:

1. Can all the forms above be submitted online? If not, which forms can be submitted online and which forms need to be filled online and/or printed then mailed out? Is there any advantage to filling the documents online and then printing them v/s downloading the PDF, filling it offline and printing it? Is there any advantage to to just mail everything together instead of submitting some forms online and rest by mail?
2. Is there an order to filling out and submitting the forms? Particularly interested in understanding the order of submission of the online forms and subsequently the printed/mailed forms?
3. For the forms that need to be mailed out, the USCIS website seems to suggest a separate envelope/letter for each form? I didn't understand this, does it mean I have a separate cover letter which I staple to the forms and then put them all into a single envelope? Or should I have a separate envelope marked with the name of the form and then put all those envelopes into a larger envelope and mail this together? Or does each form need to be mailed out separately in it's own envelope (to the same or different address)?
4. Which supporting documents are required to be submitted in original? (the USCIS website suggested that we don't mail in original forms unless required)
5. My wife (working) is applying for her mother's GC, so she will be filing the I-864 as the primary. We do a joint tax return, do I also need to file a I-864A (my income is much less than hers)?
6. I-765 (EAD) - is there any downside to filing this form as well?
7. Am I missing anything else?

If anyone has tips on common mistakes or things to be careful about while putting together this information, it would be appreciated as well.

[Attorney_6]

As this is a very extensive list of questions I am unable to respond to all of them here. Please bear in mind there are many intricacies to this process, beginning with whether filing the concurrent I-130/485 petition is possible  and the timing of it, and how that affects your parents current status.

List of USCIS forms that can be filed online can be found here: https://www.uscis.gov/file-online/forms-available-to-file-online . I would generally recommend all forms be filed at the same time, in the same format.

You are only able to file for I-131 and I-765 forms together with or after the I-130 and I-485 have been filed. For the I-864, you are only required to include a second sponsor if the primary/petitioner does not have enough income on their own to meet the HHS Poverty guidelines - which can also be found here: https://www.uscis.gov/i-864p 

No, there is generally no downside to filing Form I-765.

I would strongly recommend you call our office to schedule a consult to discuss these filings, and your options, so you understand the process and have all the information in hand before proceeding.