What I'm trying to do: Make trade route work with some penalty if there is no war and border is open & replace trade treaty with FTA, which removes penalty on trade routes

First thing came into mind was tariff system. It needs two things.

A) Trade Company income generated by connecting trade routes with its trading partner (can be replaced with trade surplus/deficit value)

B) Any ways to transfer fraction of trade income to its trading partner [could be neglected if not possible]

But I can't even go through step A. So here are my alternative plans.

• discriminate internal/external trade routes & give separate modifier
• consider number of subsidaries owned by trade partner as representative value of trade income from that trade partner
• add fees to using subsidaries owned by trading partners without FTA
• allow each empire to blockade every trade routes which is not owned by trading partner with FTA

What I want to know: Feasibility of plans & things I've been trying to do (+ any useful info or recommendation would be appreciated)