1.You need to research:
Personal Shield
AND
Disruptor Gun --> Devastator Cannon
AND
Light Disruptor Beam --> Medium Disruptor Beam --> Small Disruption Shield
This allows you to research X-Com Armor.
2. No special abilities as such, if you hoped for any.
3. It's nearly twice as hard as Megapol armor and weighs almost nothing (1/8th of Megapol suit weight or 1/5th of Marsec suit weight).
4. It's really hard to describe. A picture of it can be found
here, near the bottom of the page.