1) add custom scripts trigger commands which should trigger custom made scripts when certain conditions are met (at the beginning of a campaign for example would be the most obvious one) = to get rid of the show-me-how inelegant way of trigerring moded scripts for the game
This already exists I believe...

3) export a script function to allow character's age testing (to allow constructions like if character_age < 20 etc) if it's not already in the game
I don't know it, but it seems likely that this exists.

7) re-enable the -show_err command line parameter too
I believe there is an option in preferences.txt which makes the game save an error log.