there are a lot of HR's that are trash and can just be traded for rare medals. any HR that is balance type should always be traded. some HR like the demon and taimanin defense HR are really good if you don't have SR defense cards.
only 1 raid boss encouter at a time. gonna finish one first before you can meet another.
for annerose, it was 7 months after the game launch or the 15th held gatcha. we are in the second gatcha already.
edit: as a reminder, mid rank rewards are locked in, in less then 2 hours. make sure you aren't knocked out of what ever rank you are aiming for at the last few minutes.