Hello!
As the title says: I want to make my own core mod. (I want your help/advice)
But the only tutorial i found was here on ModTheSims and that tutorial is pretty old.
I use Windows 10 now and I can believe that some of the sims 3 functions have changed over the years.
How should I start? I already downloaded some programs(can´t remember their names though...)listed in that tutorial.
http://www.modthesims.info/showthread.php?t=354419
I have been done som XML Tuning modding before, so some knowledge I have!
My main intention is to alter the Story Progression to let neighbors finally have babies on their own!
And maybe teen marriage and pregnancy and stuff.
Because, I have been tested with XML Tuning as mentioned above with both Storyprogression and Demographics XML´s and they have NOT get any babies yet!
Thank you in advanced for your help.

Nraas storyprogression is actually really affective on the original story progression. It also makes it possible to have teen marriage and pregnancy if you like. You could edit the game's Storyprogression XML file, which just keeps the default story progression limits (So no teen marriage, pregnancies, and whatever is not possible with the default story progression). But it does increases the amount of people moving in town, and possibly the amount of marriages and children.

Yet i'm not sure how to 'replace' the game's story progress script myself >-< Maybe nraas Storyprogression can help you out with that if you use it as a reference?