eshin economy questions

Im playing an eshin campaign and I have the feeling in not really understanding how to skaven properly. I played a bunch of ordertide campaigns on hard but this seem different.

economy buildings seem weak and food allows to bypass growth. how should I go about it ? should I forgo economic building alltogether ? are you suppose to hold territory or to be forever moving forward ? should I hold crapstacks early on ? What's the best way to have enough food ? what about the underempire ? is it worth it to do ? should I build it close by or rather far away to undermine a powerful foe over time ?

also I'm not really using eshin mechanics...