I like it, but instead of automatically spreading to size 10 cities how about an event driven model:
Event 1 (common): "Sire, Jewish merchents have asked to establish a community in our nation, what should we say?"
Option 1: "Let them settle", judaism spreads in one of your cities, you can build the three buildings and cities with Judaism have 1 more trade route.
Option 2: "They may set up shops, but insitute a tax and watch on them": juadism spreads in one of your cities, but you can't build any of the buildings or spread it youself, but that city gets +25% gold (no extra trade routes). There is a chance of this event occuring again.
Option 3: "Drive the Christkillers off!", +1 Happiness in every state religion city for a while. This event may reoccur.
Event 2 (uncommon): "Sire, the people grow angry at the jewish presence poisening city X"
Option 1: "Protect the merchents from prosecution": Get a cash reward, a jewish missionary in that city, +3 unhappy in all state religion cities (so obviously do it under free religion eh

).
Option 2: "Use our offices to cool tensions", costs money, +1 unhappy in the city.
Option 3: "Do nothing", +1 unhappy in state religion cities for a while.
Option 4: "Drive this scourge from the city!", +2 Happy in the city, cash bonus, judaism and the buildings removed, -1 happy in all other cities with judaism and diplo negative with free reglion civs.
Option 5: "Forbid this scourge from our empire!", +2 happy in all cities with state religion for a while (1 of which lingers), cash bonus, - 1 trade route in every city, diplo negative with free religion civs, removes all judaism from your empire.