Do not fear, the more we can discuss, the better we can improve ideas overall.
About (1), I talked about Romans, because I read about them but I guess other civilizations may have similar 'technologies'. About barbarian civs, that's exactly what I meant in the main post: "Civs picks will have direct consequences when/if a siege situation come into the game". In my opinion, barbarians would still be played by aggressive players which wants to brute force the match, or as the perfect complement in team games (thus you will need more synchronization with your team players).
Regarding the rest of points, I'm glad this is already planned at some point for the game
Of course, as you point out, there is still a lot to learn and think since the capture update but I am sure all together we can bring nice ideas and feedback to our nice devs.
Thanks for your compliments. I'll be glad to discuss more.
Have a nice day!