Been playing ES2 for some time and still i don't understand how this trade network system works. And having to google for guides and videos about it means it isn't explained ingame well enough.

Do i build one Trade Co and fill the rest of systems with Subs or do i just build one Co. and one Sub to balance it, how much systems do i need to have for an optimal income ? How much do i raise the "level" of the ships for each trade route ?

Do i even research trade Co.-s if near by factions don't have any Trade Co.-s built ? At one time i noticed an AI didn't want to have a trade agreement with me and i didn't understand why, than i saw he doesn't have the technology...so i ended up gifting the tech to him i could maybe increase my income.

Do i need to have an allys system in between my Trade Co. and my Sub or the location doesn't matter, if they have a sub in the "cul de sac" or the "spiral galaxy with arms" map my trade ships will stil reach them ?

Do mionr factions affect trade, do they trade (if not why) ?

In Civilization games i can clearly see the trade routes and the carts moving up and down (also you establish trade with minor factions) here i don't know what's happening and as i said, in game info is lacking to say the least.

https://www.games2gether.com/endless-space-2/forums/66-game-design/threads/20683-community-gdd-13-update-trade#post-211485

Link above is a document written by devs a year ago. It's not 100% accurate as there were lots of changes on trade since early access. But the main mechanism of trade routes is almost same today. So it will be helpful.

The best rundown I've found so far on Trade Routes is this video.

There's also a little bit of info on the subreddit as well.

Tnx for the replys guys, links were helpfull but yeah...more testing is needed to get all the answers.

And as i said all of this is not explained in game, not by a long shot and i think Amplitude should do something about it in the forseable future.

Distance between HQ's and subs is a major factor in their profit.  Also, it pays to build hq's and subs on planets rich with luxuries so they'll increase those incomes more as they gain levels.  Researching techs to increase your star system trade value increases the profits reaped as well.  It's possible to get some pretty absurd trade values on your systems (somewhere in the neighborhood of 400%, maybe?) so if setup properly trading companies can bring in piles of dust and luxuries.