Well in the interest of completing the tree as you said, I will compromise a bit on the ITR but I will hold on the finisher. I think this a version that can go into balance testing, and it can always be tweaked.
Tradition Version 1.4
Opener: +3 culture in the capital. +1 food in the Capital for each policy of Tradition taken (including this one).
Aristocracy: +15% bonus to wonders, +1 Global happiness for each National Wonder
Legalism: Palace gains +2 science. Science buildings in the capital generate 5% more science.
Landed Elite: Borders expand faster. 25% increased effects from internal traderoutes.
Oligarchy: Palace gains +3 hammers and a specialist slot (engineer). Requires Legalism
Monarchy: +1 Gold per Pop in Capital, Capital provides +1 Global happiness per 5 citizens. Requires Legalism
Finisher: Can buy Great Engineers with Faith. Great Person +25% in first 4 cities.
I'd also like to point out that I don't think there is a script for GP%in the first X cities. There is one for capital and there is one for empire.
It could probably still be done with custom buildings, but I'm not sure why we would make it more complicated for no reason at all.
Also we have managed to avoid first X cities this far, there must be something we could do to avoid it completely?