See clip from Attorney Rajiv S. Khanna's conference call video that addresses this question.
One of the problem with a student applying for a green card is that traveling could become an issue because if CBP stops you at the border they could say that her student status is questionable because she has immigrant intent. She could have the same problem if she is married and has applied for a green card when she tries to go for her OPT. So keep these two things in mind. You may want to time the filing of marriage and the filing of I-130 after the OPT starts and not travel until the green card is actually in hand.
Looking at the Visa Bulletin which is a monthly estimation from the State Department of the dates that will be available in the following month, the latest one which is January 2015 (http://www.immigration.com/visa-bulletin/visa-bulletin-january-2015), and if we look at this in F2A category for Nepal which is “All Chargeability Areas Except Those Listed” right now they are backed up to 15 April 2013. At least they are backed out for less than two years. It is reasonable to expect that the green card within a couple of years maybe two/two and half years. But these dates can go up and down quite rapidly. Keep that in mind.
Typically Form I-130 is filed. Once that is filed you have to wait till the priority date becomes current. When the priority date becomes current you file I- 485 and with the I-485 typically you file an application for employment authorization for advance parole to travel. Once you get the advance parole you can travel. At that point student status is no longer an issue.
So in a nutshell that is the process. When the time comes, the I-485 gets approved and she gets her green card.
Answer to question 2: That is incorrect there is a wait time.
Answer to question 3: That can happen only if the priority dates are current.
Answer to question 4: I-130 has to be applied before I-485 or will simply be returned and you will lose your fees and will have to file again.
Answer to question 5: It does not look like it, but you can apply for H-1 because H-1 is immune from the problem of having a green card pending. F-1 has a problem and shhe can’t travel. But H-1 will not have that problem. I would suggest in this April apply for her H-1. That way you are good for three years and you can apply for her I-130 right away. She can travel freely once she gets her visa stamping. So it is a really good way to go.