Doubts with Strategies

I never used strategies, and i was searching something some strategie to learn about them, i have some douts with the real value of the improvements of strategies.

Imperialism- The lowest price for units ¿how much it is?
MoS- ¿Wich advanced stealth units? ¿How much less powerful attacks of main units?
Hibrid war- What it do?

I see they are many strategies, any info about new units, how less or more powerful units are, its welcome.

This might help http://atwar-game.com/home/units.php

Thank you!