2) The Fremen often go for a long time without adopting a religion. I really think we should give the Fremen a free Shai Hulud Mystic when Shai Hulud is founded, whether it is founded by them or anyone else (usually the Bene Gesserit). I guess this is quite a simple Python change, but I don't know how to do it.
Agreed, I've made several suggestions about this before.
I'm not sure if a free Mystic at Faith is the best; that would lead to Fremen going Shai-Hulad every game. Whereas what I think we want is for them to go Shai-Hulad sometimes, and Mahdi other times.
Also, it detracts from the first-to-found advantage if Fremen are guaranteed it so early. One of the advantages is the water and culture bonus from the temple, that can be valuable early on.
My proposal would be:
a) Change one of the Fremen starting techs to Mysticism, so they race Bene Gesserit for Shai-Hulad. AND
b) Give Fremen a free Shai-Hulad mystic (by Event) when they research Jihad IF Mahdi has already been founded.
[Otherwise the Fremen founds Mahdi]
Event is certainly the best way I think to trigger this sort of thing (free units on a particular condition)
[On a semi-related note, the Shai-Hulad cathedral was intended to give +1 happy with Fremen Water Debt resource, but this doesn't seem to be happening (anymore)? Or is it on the base temple and I didn't notice?]
3) We need to somehow make it impossible to have both House Shield Generator and Force Shield buildings in the same city simultaneously.
Agreed. In Warhammer we have a bunch of building blocks like this, I think using Python. There are 4 chaos gods, and you can have a temple dedicated to one of the four, but that then blocks the other 3 temples.
You could ask Psychic_Llamas or Orlanth how they do it.