Just Paul

No idea.  That is up to you and your girlfriend.
 
You haven't provided any meaningful details of the relationship. 
 
It is pretty clear that you both haven't done the research to see what fits for you both.

Contact the consulate that issued the Visa.

Contact the consulate that issued the Visa.

Scan is fine.
 
Don't know about Nepal consulate scheduling. I'd guess a few weeks.  Ask in the regional forum?

Two quick thoughts.
 
A CR is good in that a refusal at the consulat can effectively be appealed via the USCIS reaffirmation process.   
 
A K1 is good if you can handle the risk of refusal and if approved, with your spouse, handle the wait and delay of getting an EAD, AP and becoming a participating member of society.  6 to 9 months of Netflix and chill can be a lot of stress for many relationships.

Technically yes.  But as long as they have sufficient ties and plans to return they should be good.
That is illegal work on a visitor visa.  Suggest you have a better plan.
 

OP - yes you can file.   But you should have met several times before filing any petition.  You want the strongest possible petition.  Invite your US Citizen girlfriend to join us here and we can wolk her thru any issues.
 
And read the guides.  Blue bar at the top of every page.

I personally chose K-1 for me (the beneficiary) and my husband knowing full well what we were getting into because:

1) We couldn't bear to spend any more time apart - this is probably the biggest reason why we chose K-1
2) We were confident we weren't gonna get denied - we had more than enough evidence of a bona fide relationship to qualify, I'm very organized with documentation (LOL), and I'm confident in interviews. A lot of K-1 applications trip at the finish line because of failing the interviews due to lack of confidence or failing to answer questions, giving the impression of fraud.
3) We're NOT eager for me to start working and/or travel overseas, so the EAD and AP delay were of no consequence to us. My husband makes decent money and we have a simple lifestyle, and we benefit more from our current arrangement of him being the breadwinner and I the homemaker.
4) Despite the lack of employment and such, I'm not bored or anything like that. And this arrangement makes our relationship easier rather than stressful. (Still pondering on how the "Netflix and chill" status can cause issues?) 😅
There are many other substantial activities to keep you occupied aside from a job, you just have to actually want to do something relevant with your time - learn a new skill or further develop one you already have, educate yourself on a topic of interest, etc. Whatever you choose to achieve in the meantime can also be aimed towards future employment.

So as you can see, choosing K-1 for me was for very tailored reasons; and I understand that most people can't relate as much. I believe that the K-1 path is better for you ONLY IF you feel as strongly as I and my husband did about these 4 points of consideration.

Good luck on your journey and I hope the route you take works best! 😊

1. Yes. 
 
2. 9 - 5 = 4 < 6  doubt any airline would board her even if the visa was issued.  

Most members can complete it on their own unless they have criminal or other eligibility issues.
 
Lawyers and document services make a lot of mistakes, pointed out on here, and cause delays.   Make sure you have one that does Family Immigration and not Employment Immigration.
 
If you can follow the checklist you will do fine.

Fall 2018.   What is a temporary US visa?  The I-551 stamp on a CR1/IR1 VIsa is good for a year.

No.  Residency does not equal passport.   Some people have dual nationality by birth or other methods. The best advice to to interview and hopefully the CO will recommend a waiver  OR maybe Nigeria will get off the list. 
 
 

You fill out an I-864 and your sponsor fills out an I-864 and their spouse fills out an I-864a

Just do a renewal.  You will be keeping your name.

http://www.philippinesmiami.org/philippines-dc/consular-services-dc/faq-dc/#passport
 

You are fine since you hold a Pakistani passport.  You are classified as a Third Country National.  When you interview and upload to NVC just be prepared that you will need to upload or have documents from both countries.  

We paid for our green card prior to leaving Mexico and received it 3 weeks later.  It can take upto 4 months.
 
Your visa stamp is good for a year and acts as a green card.   We came in on a sunday and was back in Sonora on friday.

The issue will not be at the NVC.  It is at the consulate.

You can marry anywhere to be recognized by the US.
 
Some people hold multiple passports.

First off I did the same with my passport (got the new one days before my interview) and had no problems.
Second, I went K1 and I'm still regretting it. (and I got my AOS done fast). With today's wait times  for EAD/AP and AOS fees I would go CR-1 if I had to do it again (please don't ever make me do this again). Unless you are ready to do some serious couch hanging and Netflix watching.

You process along like normal.   Things can still change.   The co can also recommend a waiver at the interview.

Since you are Pakistani you are not subject to the Kyrgyzstan ban.  Interview where it is convenient for you and where you have residency.

Your brother's wife will need to do the I-864a. If they file Joint = Yes.  If they live in the same Household =Yes. If they live in a community property state= Yes. Make sure you have the tax transcripts.
 
If you do not submit it then the CO will issue you a 221(g) and as a DCF they may require you to bring it in later rather than submit it by email or dropbox. 
 
DCF isn't processed like other spousal visas.  It is best to be over prepared and get it done on the first interview.  COs do not see many of these and you don't want any issues.
 
File in you timeline and consulate so we can see your info rather than having to research your posts.  Fortunately you are London so the wait isn't that bad.

Find a better job or second job.   You can get a co-sponsor.

If you can visit on ESTA it makes the wait easier.