Ok, I will give it a shot. I've been in PH for several years using a Balikbayan.
Q1-2: All I remember is that there are a few step in Manila. They should have told you the steps. Review the info on the consulates website.
Q3: Yes, that is my understanding. The visa doesn't expire, but the card does every five years. There is an annual report every Jan-Feb.
Q4: I use a VPN showing my location as being in the US (both phone and computer). I use Xoom, and I have not had a problem in over two years. I transfer USD to my wife's BPI USD account. VPN set to a US server.
Q5: Yes, I have had no issue with any of the websites you mentioned. I have had no issues with SSA, IRS, banks, brokerages, and etc. However, it is important that you maintain a US phone number for verifications. Some sites you can use email or app notifications, but some do not. See Q7.
Q6: Pick one. I would use it before you leave to make sure you understand, and you are happy with it. My VPN service is ok. Make sure you can install it on your phone and/or tablet as well. With Netflix, you play a game at times. Every once in a while they will detect the use of VPN, and you will have to change servers. My wife watches the Good Doctor (not offered in the US) on Netflix, and we have had to change the servers from Portugal to Germany to Israel to Australia to now, New Zealand. Watch a few episodes and the proxy service warning comes on. You change servers, and the games resets. Your experience will be different with each VPN service.
Q7: I don't know if it is the best, but Google Voice works for me. I have no issues with authentications. It acts just like a US number with calls and texts to and from.
Q8: Yes, it will cut off. The number is cutoff from your provider (Verizon, TMoble, AT&T, etc.) Port the number to Google (and pay the fee) before you go to make sure it works. The number will work again once ported, but only through wifi (Google Voice app) if your phone doesn't have a data plan.
Q9: I have a PH local number and data plan through Smart. It is $15 for 90 days or about $5 a month. The local data allows me to use the Google number anywhere I have wifi as well as anywhere there is cell service. The local data plan and number will make your life easier.
The only thing weird to happen to me with Google Voice is that every once in a while it wants to re-authenticate my phone number. I found that logging into Google voice using my computer and VPN (Seattle), it goes away on my phone.
Secondly, if you travel back to the US or visit another country like Japan, you can use an eSim service like Airalo for data temporarily assuming your phone can do eSims. That allows the phone data as well as letting Google Voice to work.
Not mentioned in your list of Qs, but you should have a US physical mailing address. If you don't and you have a brokerage account, they (Schwab, Fidelity, Vanguard, etc.) may hunt you down and give you grief. I know from experience.
Hope there is some help somewhere in all that.