marrying foreigner, living abroad

I am US citizen and missionary (2-1/2 years) in Rwanda and engaged to an African (Burundi). He works for the church in Rwanda (East Africa). We want to marry in USA with my family and return to finish our work for a 2-3 years before we return to USA (Houston, TX) to live. We are trying to figure out the safest way to marry and then get my fiance permanent residency in USA, but be able to live in Rwanda for the next 2-3 years.

QUESTION 2: Should we get a fiance visa )how long does this take), marry in Houston, then file for change of status? Will they let us do this if we are not immediately living in USA?

Should we marry in Rwanda, then travel to re-marry in USA on a tourist visa for my fiance. Then, return to Rwanda and apply for his Green card (how long will it take to clear?)

Which will better guarantee him Green card, but allow us to marry in US, return to Rwanda to live and work for a few years, then live in USA?

My first concern is which will guarantee him Green Card. Second, would be cost.

With either way, what are all the forms and in what order, do I need to apply for them?
Are there any things we need to be concerned about?

QUESTION 2: Oh, legal documents here all conflict on birthdates because people try to get into school late. His passport has wrong birth year (1980). His birth certificate and ID has correct year (1978). Does he need to go correct the date on his passport to make documents consistent or will they go by birth certificate? (not easy but possible)

Please advise. How much do you charge to help file immigration documents? Thanks!