Saeviomagy
Adventurer
First up: powers work just fine outside of combat. Also don't feel bound by stuff like them restricting targets to creatures or things like that. If your wizard wants to fireball/thunderwave a door down, or your rogue wants to use steel shards to blow out a roomful of candles, you as a DM have the power to say "yes". OTOH, unlike 3e, it's made a lot more clear that a player can't say "I dig a hole through the stone wall by hitting it with my greatsword: I go at 10 feet per round according to the damage I can deal" and expect you to suck it up.
In situations that the rules weren't written for, feel free to say "yes that works" if it makes sense.
As for essentials: in part, it's errata. The rules compendium contains pretty much everything you need to DM the game, and includes basic rules errata (skill DCs, stealth/perception etc).
Heroes of the fallen lands has a bunch of new stuff that your players can use, some of which is errata, but it's mixed in with all the new classes, so it's not really a good reference for existing characters.
In situations that the rules weren't written for, feel free to say "yes that works" if it makes sense.
As for essentials: in part, it's errata. The rules compendium contains pretty much everything you need to DM the game, and includes basic rules errata (skill DCs, stealth/perception etc).
Heroes of the fallen lands has a bunch of new stuff that your players can use, some of which is errata, but it's mixed in with all the new classes, so it's not really a good reference for existing characters.