• 1) Solar Burn. And his lighting the ground on fire counts as Solar damage. You either need a Bubble with Armor of Light, or nearly full health and lots of jumping/gliding (34s probably can take it a bit better than the 33s I played as).
• 2/3 Idk, but would like to know myself, esp the latter.
• 1st Round (Hive, Trickle) pretty easy. 2nd Round (Cabal, Small Arms) can be a pain, use Red Death, it helps quite a lot. During the Objective waves, try to spawn-nuke some enemies. 3rd Round (Cabal, Exposure) is not that bad. Be sure to conserve Heavy for the two Targets. 4th (Hive, Arc Burn) is hell on earth (okay, Reef). The first wave is doable enough, only 2 Boomer Knights and some Explodie Thralls. Second and third have multiple (major) Wizards and Boomers. It is absolutely imperative that you nuke the Wizards with Arc or Solar (tracking) rockets/HMG. Knights can be dealt with, if you manage to not get blindsided. If you're feeling brave, even with an Arc Shotgun. It also tremendously helps to have a single person wait on the right side of the area (looking from the entrance) to get the single Objective that will appear there, while two hide on the far left and get the left/middle ones when they pop up, invis/Bubble is handy here. The boss is like 10x easier than Round 4. The main point is what I mentioned above. Take cover on the far left, it's relatively safe there. Focus on Ogres/Wizards whenever they come up, and then take out the other adds before firing on the boss. Repeat until either you or him are dead. Black Hammer is quite useful here. 5/6 Have yet to play this myself, so nothing I can say there.

Even if I only really answered 2 questions, I hope I still helped you.