In the beginning of the movie, when we see all the clocks, there is a shot of framed newspaper clippings (the mansion burned down on August 1, 1962). Marty has probably read this at some point.
Doc's address in 1955 is shown as 1640 Riverside Drive:
Doc's house we see in the beginning of the movie, in 1985, seems to be the garage of the mansion:
In regards to the movie:
So how was Doc Brown's reveal of a DeLorean perceived by 1985 audiences? Was it seen as a joke? An eccentricity of Doc Brown? A symbol of luxury or frivolity or stupidity?
The DeLorean fits with Doc Brown, thematically speaking. Everything you say about the car:
Notorious for poor quality, being badly made, and a huge expensive ...
He knows where Doc Brown lives in 1985. There's no guarantee that he lived in the same house 30 years ago. Indeed, it seems that he didn't, because once Marty finds his address, he has to (try and) ask for directions to it.
Marty: Do you know where 1640 Riverside--
Lou: Are you gonna order something, kid?
He wouldn't need to ask where 1640 Riverside was if ...
Adding to the previous answer which is essentially correct that Marty didn't knew the previous address. It may be because of following reason:
The 1985 Doc Brown lived in a house which was way smaller than the mansion which Doc has supposedly owned back in 1955.
Maybe Marty knew that the mansion was burnt down and Doc who was once wealthy went broke.
This is the logo of a real company called Fox Photo, who sold photographic equipment and developed photos, back in the days before digital cameras. If their logo seems unfamiliar, it's probably because they went out of business in 2001. (I must admit I'd never heard of them either until I started researching this question.)
Their appearance in these two ...
There are 2 different timelines at play here. Let's call Marty1 the Marty that we know and love. He goes to the past and creates timeline 2 and changes a bunch of things which are now part of a new timeline. People from his timeline now are not the same and may not even exist. Which is why the people in the picture are disappearing.
Luckily Marty1 doesn't ...