[Disclaimer, I am a noob in Eve and this is just the culmination of my admittedly limited experience. For more detailed and accurate data, check a more knowledgable player or perhaps Eve University. Other Capsuleers are encouraged to correct or add on.]

For passive buffer tanks, shield extenders are used in combination with what equates to shield hardeners in Dust (though they take cap rather than have on-off durations). Low slots are almost always used for damage mods and fitting mods. (There are almost no shield mods in low slots, and the ones that exist have bad ) .The idea is to have high buffer and higher dps in order to out last the enemy. (This is the opposite philosophy of armor buffer tanking, where you hope to out last the incoming damage while applying your own. This is because damage mods and armor mods are low slots)

Though used more for PvE, passive rep tanked shield tanks are also used. These take advantage of the shield regen mechanics, where that shield will always regen for the same amount of time, so having a 100hp tank and a 10,000 hp tank will always regen in the same amount of time for the same ship. This, in combination with a huge buffer tank (shield extenders), regen mods (usually shield power relays because of the lack of need for capacitor, similar to Dust's shield rechargers), and resistance hope to curb the damage done from rats (again typically this isn't possible in a PvP setting).

Active tanking requires the use of shield boosters and ancillary shield boosters. Shield boosters require a lot of capacitor to use for extended periods of time but provide a decent boost to shield hp every cycle. They typically use of a cap booster to keep cap level up (mid slot). Ancillary booster work in the same way, providing a much larger boost to hp, but require A LOT more cap. Thankfully, they can be loaded with cap booster charges instead of relying on your own cap (though there is a crazy long reload time). Another mod that is important is the shield boost amplifier that boosts the amount of hp the shield boosts give per cycle. Lows are again used mainly for damage mods.

All in all, there are almost no shield mods for low slots, and the only ones that are available reduce base shield hp or max cap.

Clearly you've never encountered an incubus duo in PC. Well, at least pre-Charlie.

A vehicle should be better than a dropsuit in firepower, but require multiple people to man. I honestly feel like vehicles are in this state of being unnecessary, since they do nothing a dropsuit can't do. But they should be as effective as multiple dropsuits, while taking multiple dropsuits to man. Also, this means we can make it take multiple AV to shoot down.

To Grey: I feel like ADS were supposed to be Apache's, but were gone about it wrong. A true attack aerial vehicle would be a light aircraft, basically a LAV in the sky. As it stands, we need a dedicated aerial attack craft. ADS can fill that role, at least until Legion comes out and we can create new content. As far as incubi being the answer to everything in the sky, yeah that's the point. The incubus is the vehicle killer, to include dropships. ADS should be Apache's sacrificing transport for more attack abilities. SDS are Huey's, door guns to support infantry, but mainly focused on getting troops from one place to another quickly. scouting is easily done with refurbished SLAVs. Everything has it's place.