hey merku welcome
I was the same as you.
Reading alot but just lately i popped out and start posting.
About your TLDR:
-How long do skirmish mode games last?
-Will there be a mini-LAN-based campaign?
First question is answered in this question
Q: How long does the average skirmish match take?
A: A two-wave medium difficulty skirmish match takes around 30 minutes for the average player.
For the 2nd question there is a campaign.
You can find your answer in this FAQ Question perhaps
Q: What are the available Victory Conditions?
A: There are three ways to play Kingdom Wars: the short campaign (Unification War), the long campaign (Realm War), and the epic campaign (Total War). In the short campaign, players start with one major town and their goal is to conquer the other three major towns of their race as well as 50% of their race's minor towns. In the long campaign, players start with one region - one capital town and two minor towns, and their goal is to conquer one of the other two races and to conquer all of their major and minor towns. In the epic campaign, players start with one region and their goal is to conquer every major town on the map for all three races, as well as 50% of all the minor towns.