1. Yes, Maggie is definitely at the top of the list. Still, no proof, but remember that Maggie is a nickname for Margaret (Margie). That, along with the surname of 'Robertson', increases the possibility that the Informant was his wife.
2. he 'M' means married, not male.
Look CLOSELY at the actual 1920 census record. You will see that the family is actually on two pages. On the first page, there is Family 49 (#70), Head-of-household,
Peele Edwards (written like that). Then, there is
------ Janie A., the 'wife' - indexed 'Jame', but looks a lot like Janie to me.
------ Minnie, the daughter
------ Mogie (Magie?), the daughter
------ Mary, the grand-daughter
On the next page is the 'rest' of the family
Edwards, Johnnie, 'daughter'
-----------, Willie, 'daughter'
-----------, Sarah B., 'daughter'
The last three members of the family had the surname 'Edwards', which could indicate a transcription error. Maybe the given name and the surname were 'transposed'.
Also, the fact that 'Peele' is a valid surname, shared by at least 30 other people in Titus county, should be investigated. Was this error intentional? Was he called 'Peele' Edwards?
[File that bit of information. It may become helpful if you ever want to do more research on the Peel(e)/Edwards Family.]
3a. No, they are NOT saying that about Mt. Pleasant, which is an old town - the county seat. I believe they are saying this is the Negro 'section' of town (?). Mt. Pleasant is an interesting place - get more information from the city's website (mpcitydotnet).
b. I could not find a Jefferson Highway, but found the current day Jefferson Ave. In the history of the town, there is mention of a Clarksville to Jefferson Road. Clarksville is to the north (Red River) and Jefferson is to the southeast (Marion county). This could have become the Jefferson Highway mentioned in the Census. It could even have become the current day 'Jefferson Ave'. Only a detailed history can put the puzzle pieces together.
c. The (3) means it was repeated three times - like birthplace, birthplace of father, birthplace of mother. If ALL were born in Texas, for example, I abbreviate it as TX(3).
You can find more about the Railroad in Texas from the Handbook. It's the number one online resource for Texas History (in my opinion).
One last entry - a Preston Edwards is living with his brother (Joe) in 1880 Harrison County. THIS Preston was born in Texas. His parents were born in NC, per the census. The wife, Louisa, was born in LA with both parents born in NC. There is one daughter in the household.
Interesting household. Look at it in the 1880 census! There is another family in the household that is not indexed as the same family. Was this another census transcription error?