So glad to hear you've enjoyed playing so far! I love your idea for keeping track - I'm planning a play sheet and that's some real inspiration!
To answer your questions:
The game was designed so that you're always moving forward. As such, you can't return to a previously explored room. While those are the standard rules, there's no reason why you couldn't make it a house rule. Off the top of my head it could be a skill for a new class (Scavenger, perhaps?) or a variation on the Shimmer spell that enables you to translocate momentarily to the previous room. That's definitely given me some food for thought!
With respect to combat, you only take damage from the Monster you're currently attacking. If you wanted to ramp up the difficulty you could certainly play as you describe. Thanks for the spot - I'll update the rules to clarify.
Thanks for taking the time to play and comment, and good luck in The Ruins!