I added the 100% gold bonus objective and the ability to lock in guards to the suggested features list. I think when the player locks in a guard, the guard should be able to open the door in a minute or more. Just like how knocked out guards are either revived by other guards or wake up after a minute. Otherwise the player will be able to "eliminate" all the guards and make the level too easy. Although that might also be a fun level objective: ambushing all the guards ^^
I won't lock any existing unlocked characters. I could unlock a random character skin when the player meets all bonus objectives. Adding a completely new character to the game takes a lot of time, and I prefer to expand the gameplay first. But it is a very interesting suggestion. Please let me know if unlocking playable existing character skins is interesting enough to include in the game.
I'm not sure about character specific abilities. They sound interesting for replayability, but I don't want the level difficulty to depend on specific characters. I did considering character-specific abilities such as: ability to hide in more places, ability to climb through windows, a very silent character and a faster lock-picking ability.
Speaking of hiding places, I think I'll add more hiding places such as in barrels and under beds. I excluded those hiding places, because the current last level became too easy to complete. But if I include a bonus objective "no hiding", it could be used by the player as either an easier victory or an additional challenge.
I can't reproduce the candle light bug. I've visited the exact same location as in your screenshots, but the candle burns correctly here. I will keep an eye out for when I see an unlit lit candle happening.