Okay, to answer your questions:
1. As you increase the difficulty, enemies have more health and armor/shields/barriers, and enemies deal more damage.
On Hardcore and Insanity, all enemies get a protection layer (shields, armor, or barriers), except for enemy combat drones and the mechs on Lazarus Station. On Casual, Normal, and Veteran, only elite enemies had a protection layer.
For example:
- Vorcha and Loki mechs have no protection layers on Casual to Veteran, but have armor on Hardcore and Insanity.
- Collector Drones have no protection layers on Casual to Veteran, but have barriers on Hardcore and Insanity.
- Geth Troopers and Blue Suns Troopers have no protection layers on Casual to Veteran, but have shields on Hardcore and Insanity.
Elite enemies -- such as Blue Suns Legionnaires, Collector Assassins, and Geth Hunters -- have protection layers on all difficulties.
Super Elite enemies or boss-type enemies -- such as YMIR mechs, Geth Primes, or Harbinger -- have two protection layers on all difficulties.
2. Best bonus powers for Adept:
- Energy Drain (to deal with shields)
- Stasis (1 point) to help with YMIR mechs and some other enemies occasionally
- Warp Ammo for the extra damage to enemies lifted by biotics
I prefer 1-point Stasis.
Warp Ammo deals extra damage to enemy health, armor, and barriers, up to +50% of base weapon damage (Heavy Warp Ammo). That listed damage is doubled when hitting an enemy lifted by biotics (+100% for Heavy Warp Ammo for example).
3. I will deal with this in my next post.
4. Biotics such as Pull, Singularity, and Slam will not lift enemies that still have protection layers (shields, armor, or barriers). But they will stagger enemies. Singularity in particular can hold an enemy in place while they have protection layers and will drain the protection off over time.
Most powers with a crowd-control aspect will not work on enemies with protections. For example, Pull will not lift enemies, Cryo Blast or Cryo Ammo will not freeze enemies, AI Hacking will not hack mechs, and so on.
I may deal with this topic in my next post.
You may choose to bring along squadmates that can deal with protection layers. Miranda has Overload (shields) and Warp (armor and barriers) for example. Mordin has Incinerate. A lot of squadmates have Overload. Tali can learn Energy Drain(shields), and Samara has Reave (armor and barriers).
As an Adept, I prefer Miranda for her Warp to detonate Warp bombs so I can continue shooting or setting up another biotic combo or just controlling the enemies with another Pull. I like using both Miranda and Thane together actually.
NOTE: By default, Warp has a 12-second base cooldown on squadmates, but Unstable Warp has a 9-second base cooldown on squadmates.
Good squadmates for an Adept (no particular order):
- Garrus (Overload)
- Miranda (Overload, Warp)
- Thane (Warp, Throw)
- Jack (Pull)
- Jacob (Pull, Incendiary Ammo)
- Samara (Pull, throw, Reave)
- Morinth (Pull, Throw, Dominate)
- Mordin (incinerate)
Only occasionally useful for an Adept:
- Zaeed (Disruptor Ammo for synthetics and overheating enemy weapons)
- Tali and Legion (AI Hacking for Geth)
- Kasumi (Flashbang) Note that her cooldown in her passive does not work
Forever useless to everyone:
5. NEVER LET SQUADMATES USE THEIR OWN POWERS OF THEIR OWN FREE WILL!!!
Always... and I do mean always -- set squadmate power usage to manual so you can control when and how they use their own powers.
Note that squadmates will always automatically use the defensive powers Fortification (Grunt), Barrier (Jacob), and Geth Shield Boost (Legion). This makes them useless in combat. This is why completing Lair of the Shadow Broker to get access to the squadmate power reset terminal is important.