Couries vs Network vs Spy Network vs Contacts vs Fame etc

There's a lot of different backgrounds and merits that allow for the PC's to gain information about a lot of things, I'm going to try and alleviate any confusion here.

Couriers are a group of your trusted messengers who you send information out with, it is mostly word of mouth and this information could become misconstrued, or intercepted. However it is the fastest way to send information to your clan mates in other domains, or cities. This is all used via clan specific secrets and other clans getting ahold of a your clans mouth piece could cause your final death or worse embarrassment to your clan.

Contacts allows you to access information on influence use, want to know if someone is pressuring the local friar into denouncing your favorite pawn, use contacts and find out if influence was used. You can also use it to figure out if it's possible to move up into the next stage of influence in the game. (Seats are limited in the influence game!)

Network allows you to send and receive messages through certain locations (named when you pick the level of network) that you have minions in, other kindred don't even have to be involved in the info sharing. Network also allows you to maintain levels of backgrounds in other cities, although the game will not take place in other cities as a whole, some players may wish to have their character travel to another place during downtime, giving them access to backgrounds they normally wouldn't have.

Spy Network 2 Point Merit ( Vampire: The Dark Ages -- Page 276 )

The merit - "You begin play with access to a group of mortals who frequently bring you information on the daylight world or on faraway places. Their information is both up-to-date and fairly reliable, and they are not likely to lie to you. However, these cannot be used as Allies or Retainers (unless you have that Background, too); they have their own aims. The more they know, the better they can search out relevant information and pursue useful rumors -- but the more damage they could do if they ever betrayed you. A spy network might be anything from a peasant family to a coven of witches, a merchant family's underlings, to a network of wandering lepers. What they can discover will depend upon who they are; different people move in different circles, after all."

Similar to network, however doesn't allow your backgrounds to move with you, and the information is focused as well as dependent on their "flavor"

Fame - Fame Allows you to use your local Contacts, Influence and Resources and push it beyond local borders into the surrounding kingdom. While Network allows you to pick cities you've been too, Fame forces you to stay in the local area and spread from there. Network also gives you retainers in other areas, so the people you have in England are not the same as the people you have in Rome. Network also does not allow for the use of influence in other areas where Fame does.

If the base play area is the County of York, how does this effect backgrounds such as fame and network? I mean if influences can reach a whole county, it wouldn’t make sense that network/fame only reaches and additional city which is less then a county?

Yorkshire is not a whole country, just a section of one. So Fame still has uses to expand control across all of the Country, including down to London and possible across the sea at high enough levels.
This goes for network as well, though network seems to be more about establishing outposts of power in specific places, rather than the general expansion provided by Fame. With Fame your radius of control expands in all directions around you, but with Network you could specifically choose to build a powerbase in Spain, Italy, or France. I would not think it would make sense to create networks inside of York for most characters, since they are relatively close by. However, if someone wanted to be able to control their lands but still travel to York frequently, they might build a Network between the two areas to ensure that their retainers will still be available and their herd will still be tappable, etc. It would not expand your influence range in that case, but it would be more frequently useful since travel times can be a significant bar on people with domain far from where the session is taking place.

It also allows you to gain information on things going on outside the domain, want to know who the new kid in town is, find out where he's from and you've got network in a place closer than York, you'll get information faster, as well as rumors and weaknesses...