Factions like Skaven and Tombkings on the campaign map - how to make them fit into the concept and technical limitations of human empires

The purpose of this thread is to discuss the inevitable problems which occur when trying to depict non-human races as a faction on the TW campaign map.

I want to begin with the Skaven, but the discussion is open for any kind of input.


ISSUES (gameplay-relevant differences to human societies)

1. Skaven do not generally live on the surface and build or maintain settlements above ground
2. Skaven maintain extensive underground networks and espionage which allow them to see without beeing seen
3. Skaven have no diplomatic dealings with other races, temporary alliances of convenience at most
4. Skaven do not peacefully trade with other races and have no monetised economy
5. Skaven soldiers are not payed, they fight because they are dominated by stronger Skaven or because they lust for plunder and murder
6. Skaven hardly have any use for industrial products or luxury goods besides what can be eaten or made into weapons
7. Skaven reproduce a lot faster than humans and don't really need housing
8. Skaven are hardly affected by plagues due to their short lifespan, high reproductive cycle and general resistance, but carry plagues everywhere they go

POSSIBLE SOLUTIONS

1. Possible motivation to hold cities after conquering them: Using the inhabitants as slaves. Upon a successful siege, Skaven should not have the option to "occupy", only to "plunder" and "exterminate". They should keep civil order through fear alone, maybe have the option to "sacrifice" (read: massacre) inhabitants to restore order
2. Skaven could be able to recruit spies at (almost) no cost and receive huge bonuses for them, maybe even disable FOW completely for them?
3. Make it impossible for Skaven to have alliances
4. Make it impossible for Skaven to maintain trade agreements. If possible, restrict trade to Skaven settlements
5. No idea yet
6. If possible, restrict trade to raw materials and basic food
7. Use an "underground colony" building which can be upgraded and radically improves pop-growth
8. Give all Skaven characters traits which increase their chance to become infected. Make Skaven settlements immune to plague effects or counter them by balancing them with higher pop-growth.

[1] The Sundering: Rise of the Witch King - Sons o - Mod DB