I'd like to know your opinion guys.
First some thoughts on your more set-in-stone changes:
Swords to 15: This is a good change, Swords are too OP compared to Horses right now IMO. Lessening the raw strength difference will help Horse strategies compete despite their many problematic disadvantages.
NC no slot, +3/25 instead of slot +30: This seems like a big nerf to me. I think this mod rewards early wide growth enough, punishing the tall NC like this seems sort of like piling on. I would increase the % modifier instead of decrease it if you're going to take the slot away, and I'm not crazy about the flat science.
AI Beliefs: AI should be more likely than it is now to take Tithe, honestly. I know I harped on this before but the AI never taking it sort of centralizes the human player's game.
Speculative changes:
I like the idea of more merchant and engineer slots moving early, it harkens more to the idea of specialized cities which is a good thing. Also encourages generation of GMs which you don't see too often. I would say the Markets needed it more though, Workshops are already pretty good. Maybe you could split the difference and give the extra Engineer slot to a less spammable building like Stone Works? You could even give the merchant slot to Circuses, if you wanted it to be a theme.
I like the idea of Trading Post reform. This version might or might not be good but something has to be done and we can see how it feels in play. I would lean towards giving them the +1 at Guilds too, make them more close to too good so people use them and we get a feel for them.
I don't like the lessening of % bonuses to gold in exchange for flat gold. As I said before I think wide play is good enough, and these sorts of bonuses inhibit specialization of cities.
Big Ben and Merchantilism nerfs are well deserved. Flattening of the exchange rate also seems wise.