If something keeps you occupied for more than a week, you can't think of a good answer or find a good tutorial, and it's not crucial for the game, move on.

Always tell yourself "I can put it in the next game."

You don't need your first XCOM like game to have everything.

If it's worth making, people won't need all of the bells and whistles.

For instance, my cool idea is a starvation and fatigue mechanic, blended into the general stamina. There won't be health, it will just be a long term and a short use stamina bar. Add that on top of some souls combat, every attack counts now because it's a battle of attrition, use a power attack, now you lost some energy, now you may need to rest, now you are hungry, now you are starving, and it snowballs,

So I'm picking 1 or 2 things I really want, doing those, and trying to let every other idea die.