Welcome back Kulko
I haven't been able to look at the save recently but...
Darwin should always be arranged to finish on the same interturn that a research completes. It's better to delay the wonder than the tech of course, and we should take care to allow for the possibility of pollution during construction of the wonder. That kind of stuff is easier to arrange when doing 4-turn research, which we aren't going to see in this game, but still we will want to do some sums when it comes to planning Darwin.
As arch says, Atomic and Electronics are going to be the best techs to take.
Why do we delay? Well Industry might be of use to us in the short term, whereas Scientifc, Atomic and Electronics are of no use other than getting through the tech tree. In the medium term, there is one more tech which has the power to directly improve our commerce; Mass Production allows the commercial dock; we should plan to prebuild these in all core towns which work coastal tiles (i.e. Tenoch and Delhi probably shouldn't sweat over it). So in an ideal world we would research as fast as possible to Mass Prod before going for Scientific. But I think we might get nervous about the (small) risk of France doing Scientific>Darwin ahead of us, and prioritise it sonner.

Here's a little thought. Can we actually get a lot of commercial docks built as soon as that tech arrives? It seems unlikely that we could be that well organised, but if it can be done, maybe the best techs to take from Darwin are Atomic and
Mass Prod. I'll try and do some sums.
In theory, we want to irrigate everywhere, including Constan, and max out on scientists. But an extra scientist in Constan adds only 3 beakers to our economy, same as an extra scientist in somewhere corrupt like Hattusas. Whereas a mine irrigated in Constan drops our net production by 4 shields, and a mine irrigated in Hattusas probably doesn't affect our net production at all. So I'm happy to have our workers toiling elsewhere for now.
As for the diplo prospects, they don't look good do they?

I've never really been good at identifying what is affecting AI mood, and whether it can be helped, but there are plenty of possibilities... they could be angry because we broke deals with them (short alliances, interrupted trades), or because we have been at war and taken their towns (applies only to Persia I guess) or just because we are stronger than them. As you say, we have been careful to avoid using our most dastardly diplomatic tricks on some of these AI, but maybe they are just upset because they saw us do it to other people...
Now when it comes to the voting, I think some of these people will be prepared to ally with us, and some will not. Those that do ally (and ROP and MPP) should see a miraculous rise in attitude, as happened with Joan, who went from annoyed (or worse, I don't remember) to gracious just for the sake of 3 alliances.
Anyway, I repeat my advice to get a unit into every town. What we really don't want any more is people who are supposed to be our friends attacking us just because they think they saw an easy target. And even a gracious AI can fall into that trap sometimes.