Hi Bernie, With regard to the Tram Depot, the earliest mention I have found is in the 1899 Kelly's Directory where it was recorded as Birmingham General Omnibus Co Ltd and the only other listed in that stretch, at that time, between what we know as The Swan Island and the cemetery, is David Adcock at Rose Villa.
Although the label for Rose Cottage is on the left of the road on the 1905 map, I believe it refers to the buildings on the right of the road. Whether or not the land to the left of the road belonged to Rose Cottage, I do not know.
With regard to when the houses were built, as you know they appear on the 1916 map, which puts the date somewhere between 1905 and 1916. But I don't have access to any maps for the in between years. As I mentioned, the 1911 census doesn't give an indication that they had been built then.
By 1913 Kellys records more people in that stretch and in 1915 more still.
(Just found something which might be more conclusive)>>>....If the numbers all remained the same then it would appear that the houses had been built by 1912 because they are recorded on the 1912 Electoral roll as shown in the attached picture.
I'm no expert Bernie and I could be totally wrong, I can only go on what I have found..