@eclipsezeromh I do not recommend farming Advance Quests alone because the enemy spawns scale with the number of players (so you want four players for maximum carnage and the highest chance to drop Photon Boosters) as well as to sustain PSE Bursts to continue spawns. By having a +50 Threat Level and a full party of players (AI Partners do not count as full allies) you will be able to rake in more capsules for the next area (A capsule missions drop B capsules, so you want to cycle maps) as long as you can sustain a PSE Burst and optimally kill quickly and stay with your party. Splitting up is a very bad idea in these quests because the enemy spawns are limited so if you head in one direction and your party heads in the other the spawns can get split or even completely skipped which means less enemies and therefore less rewards.
D, E, and F capsules to my knowledge drop at the exact same rates as A, B, and C capsules but are generally "harder" because the cost of entry is more expensive and because the enemies are slightly tankier. One of the fastest ways you can collect these capsules is to exchange your Alliance Points for them or to use your Buster Medals to exchange for Advance Capsules.
Most Extreme Quests were meant to be "challenges" but has since been trivialized by our powercreep. I run some (such as Ruins & Oceanids 35-40) for Meseta as it is very fast and also grants me about 150,000-250,000 Meseta per run. You can also use these to clear Daily Client Orders for fighting a variety of enemies as these tend to be predictable (such as finding Bar Lodos on Ruins & Oceanids 11-15). Some of the later ones give you access to creating the "Valor Emblem" rings which provide a 10% critical chance, 1% damage boost, and a 3% damage reduction which is nice for a Fighter as they cannot use the Critical Strike (R) ring (due to it being a skill in their skill tree). In the Japanese version there is a new Extreme Quest that scales upwards with your performance (and can be done in a team) where you are given very good rewards, augments, and potentially Buster Medals as well as rewards. This is definitely one you do not want to pass up on for jumping into the end-game for gearing up.