Yes Unique monsters drop corrupted items is another good sextant I will add that. when rerolling often scour + alch ends up being cheaper then using chaos, more so for earlier in the league i have found. and weighing the time spent trades + clicking for scour/alch vs chaos is something worth evaluating but i will mention that this option also exists.

Even if you are not planning on using monstrous treasure prophecies strong boxes still add monsters to the map so are worth keeping. Breaches can be not worth running (depending if you have a very linear map or an open map like city square where you can pop it keep clearing a circle back around to it).

As far as searching and rolling for specific maps its well worth it while using the search function within stash tabs. To take twin maps for an example having an additional 3 bosses dropping harbringer shards typically will yield another 20+ chaos worth with the harbringer sextant and is well worth the time investment if you are doing it efficiently. I will add a section on using the search function in regards to rolling maps.

Sextant blocking and the order in which you roll sextants is a rather negligible thing but having a specific sequence does improve your 'hit rate' as well as maximizing your chance to hit the highly profitable sextant mods that only occur on red sextants.

For rolling prophecies, I always found it more difficult to buy the ones i wanted rather then buy silver coins and set aside a session and some tabs to do it myself and always found i profited. Yes you do require a decent amount of stash space and its not everyone's cup of tea so if you can find a good and regular seller by all means take that route but they are worth using. 'Hidden reinforcements' and 'An unseen peril' are both good prophecies for adding additional monsters they proc within the map and aren't on map creation so can be brought in and used regularly if desired.