I'd like to add to this in asking how "they" decided where the start of a road began. Was it from where the original settlement was based and branched out and if so, what happened if two villages met each other?

I'm not a historian and don't have your answer but I suggest you rephrase your question and limit to a locale such as London England. Its an interesting topic

In 1512, on Paris' Pont Notre-Dame, according to this 1898 NYT article I found on the Wikipedia page about house numbering. The page asserts "the purpose of the numbering was generally to determine the distribution of property ownership in the city, rather than for the purpose of organization.", but I doubt it, as the bridge was brand new, with 60 (or 68) identical houses.

I can only answer the question in regard to Austria and here especially for Vienna - although i do believe that the system was the same in the whole monarchy when it was started .

So the system they had was based on "Konskriptionsnummern" (Conscription Numbers) which came into use in the 18th / 19th century and were used as a way to make several government duties easier - mainly taxation, army organisation (knowing where soldiers or people who had to fulfill military duty lived), statistics for who lived where, how big are the houses and so on.

those were not organised as they are today though. So No. 276 could be next to number 739 and so on. It was a very rudimentary numbering system and not used for postage and you would not have been able to find your way based on those numbers. Plus you didst see them from the street. The old conscription number tag in my old apartment building was actually inside the house not on the street. So as orientation help those numbers were useless (if you didnt already know the area)

The change to the system we use today happend in 1862 in vienna. As for the why - i cant find a direct source for that but my educated guess is that the old system was not practical anymore for a growing city (paris which grew much faster then vienna changed their system in 1811) in which more and more post had to be delivered, new people moved in from the country side, new quaters were built and in the case of vienna the suburbs were added to the city itself.

As for the how : The system in vienna is quite simple even numbers on the right , uneven on the left - low numbers closer to city center, or oriented clockwise.

source : Anton Tantner: Ordnung der Häuser, Beschreibung der Seelen – Hausnummerierung und Seelenkonskription in der Habsburgermonarchie, Dissertation an der Universität Wien, Geistes- und Kulturwissenschaftliche Fakultät, 2004

Anton Tantner: Die Hausnummer. Eine Geschichte von Ordnung und Unordnung. Jonas Verlag, Marburg 2007,