First off, sorry to anybody who has been waiting for my reply. I've been quite busy the past few days, as you can probably imagine, given the recent flood of previews. (And as much as I love reading your discussions, I do need breaks and weekends now and then, too.

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Now, let me dig through the various questions.
Space bores you? But
there's a hexagon on the north pole of Saturn!
Yes, Civics choices are permanent, unless other events force you to revoke or change a civic (e.g. the cultural influence others have already mentioned.)
And as mentioned in my interview with Writing Bull, we are still experimenting with when and how EQ become unavailable or obsolete. If I recall correctly, in an early version Emblematic Quarters lost their effects and instead provided culture once you added another culture, but that was unsatisfying and did not give you a sense of building your own Civilization. So the specifics of this are not set in stone yet (we think we'll unlock Masonry sometime before 2021...

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As others have theorized, this isn't an increase to Army Size, but to your number of Generals. Basically, Persians are better at administering a large empire, Romans are better at having the military presence to defend it.
I'm afraid I have to disappoint you: You won't be able to transcend your neolithic tribe.
We're planning for that to be possible, yes.
Because this is a pre-alpha or early-alpha version, so not all gameplay terms are consistently implemented everywhere, and some may not even be finalized yet.
"Transcending" your current Culture will give you a permanent trait that increases the fame you gain, so if you are confident you can compete without gaining new bonuses, that can be a potentially strong play to increase your Fame.
Yes, that's planned, but would not be available at the start of the game.
I believe both of them do give +1 Administrator, but there are long-term consequences. Specifically (if I recall correctly), this Civics is the starting point of that branching path you can see on the overview screen, so your choice here determines which choices you get later.
We have some unit responses, but as far as I know, we won't be "localizing" them to your current culture (it would be rather difficult to find a Harappan or Olmec voice-actor...)
On the repetition of events, we are aiming to largely avoid this through the trigger conditions of the events. Of course, you will probably see some events in several of your games, but I think the combination of events you get should always feel different.
I don't think we change the Fame of different actions between Eras (e.g. a wonder is always the same amount), but the Fame for Era Stars declines within an Era, so if another culture snatches a bunch of Era Stars quickly after entering the Contemporary, they may well overtake you if you take a long time to gain yours. And as far as I recall, we also have some late-game Competitive Deeds.
Sorry, but it is too late for me to ask for this to be added... We already had that preview in the latest dev build I tried.

It wasn't in the Press Build, as it is not quite done at the time.
Unfortunately, I can't give you any clear answers on this. Our Game Designers have been discussing various options on how to end the game early.
Some Civics have pre-requisites of other Civics, but most do not. Also, Civics can be revoked or altered under the right circumstances... But more on that Later™.
Battlefields do tend to get larger as the game progresses, but the details of how combat works are for Later™. (I sure get a lot of use out of that alt-code since we started talking about Humankind...)
No, there will not be unit customization. Boris has laid out some of the reasons for that quite nicely in this forum before, the difficulties of creating historically authentic units if we allow players to mess around with them. However, I personally think that neither this nor the simpler core combat calculation are detrimental to the depth of the combat, as there are many more interesting inherent unit abilities than in Endless Legend. (The vast number of "more damage against certain unit type" abilities in Endless Legend always felt like one of the biggest weaknesses of the system to myself, as they did not mesh well with the hands-off nature of the system.)
At least that's the goal, but it's sadly not ready to be shown yet.
Well, we do have scenarios for the OpenDev. The big question is when and how we integrate the ability to play scenarios, how complex they can become.
You're able to conquer territory, but the goal is that you cannot outright annex all the territory of another civilization. You might still be able to get your hands on some of their resources by war, though...
Unfortunately, modding is too complex a technical subject for me to be able to give any clear answer on that other than that we've been discussing what is and is not possible.