街 is used far more commonly than 街道, and 街道 also officially means the subdivision that is smaller than 区 in a city, so 街 should be accepted.
路上没有很多人 also works
Is 上 necessary? Why not 街道没有很多人？
Yes, it is a character that connects and without it it would sound something like "The street not a lot of people".
Not impossible at all. It is very colloquial and not at all the standard Chinese i.e. 标准华语
街 is the same thing as 街道
Especially now. 加油武汉! 加油中国!