WorldBuilding: I am clueless

OK, so I have finished my novel - and believe me, it’s a long way from done or even marketable - but I have NOT devoted the time to worldbuilding.  (Can you say ‘character driven’?? lol)  That is a task I’m going to begin today.  I’m unsure where to start, though at FmWriters,  I did find some resources way back when.  I guess my planet is mostly like earth but slightly different and that totally throws me.  Really, the setting needs not to distract from the plot but since the main character is a dethroned princess and the antagonist is the newly installed Queen, and the country is at the end of a civil war, the setting is quite important.  We are dealing with humanoids (there’s a few medical differences) and no fantasy creatures at all, with a highly evolved usage of brain areas (mind control), very advanced medicine, and transportation at a stand still (lack of fuel or fuel delivery due to war, I assume).

Yep, I got a lot of work to do.  And question 2 is, how much time do I spend on this?  Are my original goals worth it?  If it could be sold at all, this is valuable to me since I have a very good sense of the sequels, but this is not my primary genre, so that’s an issue.  Hmmmm….