You Must Submit Separate DS-160 Applications
In general, when applying for a US visa, each traveller must submit a separate DS-160 application form. In your case, you are applying from different countries, which means that you will attend interviews in different countries, so it makes sense to fill in separate applications.
Companions or Not?
You state ...
The visa application process cannot be completed until you appear for an interview with a consular officer. You should probably cancel your interview just to make it official.
According to this Quora Q/A web page
You don’t need to delete the form. Just cancel the interview
appointment, if you made one. Eventually, if the submission isn’t
used, the ...
The is no official rule for how long you will be given on re-entry to the US after 5 months in Mexico.
However US Customs and Border Patrol do use a rule-of-thumb that you should be outside of the US for longer than you are in the US. So after a stay of 6 months, followed by being outside of the US for 5 months, that rule of thumb would mean you would ...
There are several points to make here.
First is that if you are a new Zealand citizen you do not need a visa to visit the US for tourism or business purposes. You can use the Visa Waiver Program to visit for up to 90 days.
Second is that the US mostly issues a combined B1/B2 visa, which allows for both tourism and business visits, if you request either a ...
You will need to re-issue your passport using the form here.
Will there be a problem in future US travels if I do so?
No, name changes/mistakes happen often so you should have no problems doing so if you explain the situation.
B1 Visa Purpose
You can use a B1 visa for the following purposes:
What is business related (B-1) visitor visa travel?
Generally, the travel appropriate for a business (B-1) visitor visa includes;
Consultation with business associates
Attend a scientific, educational, professional or business convention, or a conference on specific dates
Although you have good intentions, business visa purposes are outlined in this State Department pdf document...
And they state specifically that you cannot accept income from a US based company/entity while visiting on a B1 visa.
Purpose of Your Travel
Conference, meeting, trade show, or business event attendee
About Your Temporary Visit
It is strange that the online application system asks your for a proof of relationship, if the person you are visiting is a friend and not a family member nor a spouse. Double check that you have selected the right relationship during the process. In should be this Question 4 on this part of the application:
Otherwise, as you mention, there should be an ...