1. I've tried a couple different builds but the one I keep coming back to is thrown axes/spears. It seems easier to stay alive and also deal damage and I also love that the upgraded axe is free :). I only tried a scrap build once but felt the payoff wasn't worth making your whole deck around it.
2. when choosing the next room I don't know what "decrease enemy interruption by -33%" means.
3. not that i can think of
4. Elites/Ambush are my fav, kill all is my least favorite mainly just because it takes longer.
5. first boss yes, 2nd boss idk. depending on the build when the beholder makes flys and then the flys swarm you it can be really hard to deal with.
6. maybe a relic that adds bleed/poison to all your attacks so it's not dependant on you drawing your bleed/poison cards.
7. when fighting the beholder sometimes the flys will push you outside the arena if you're too close to the wall. I've killed the boss while stuck outside and there's no way to get back in so I had to reset.