What should I include in my cover letter for a Digital Nomad Visa (DTV) application in Vietnam, and can I start the application before arriving?

Hi, have gone through the helpful discussions and useful comments extensively, but still have a couple questions causing some anxiety/confusion, so appreciate all assistance and advice for the below;

1) What is everyone using the cover letter for? Just explaining why they want the DTV? Or as a menu of their submitted documents or combination of both.

2) will be applying from Vietnam because went to my home base country & was they didn't process any DTV's there, so looking at Hanoi - any major cons/pros versus applying in HCMC?

3) does anyone have experience with multiple sources of remote income? (Ie: I tutor remotely and also work remotely for a company based in EU). Is it better to put just the company role? Or include both to show higher overall income?

4) can I start filling out the online portal with my documents before arriving Vietnam (but NOT submitting till after I’m in country) ?

5) and would a ready to start rental agreement for 6 months that is dated to begin for when I arrive in Thailand with the DTV ? (Have found a landlord and place to rent, but didn’t want to start prior to being approved)

*otherwise, I have 6-9 months of invoices/payments from both jobs & 6-9 months of more than the 500k required as well. Along with letter, contract etc from my employer and 4 months of invoices and matching payments from my remote tutoring. And will have ofc the hotel booking, and such paid and sorted before arriving in Vietnam.

Much appreciated in advance!