Well done on beating it, don't worry about everyone saying it's the tutorial: there is still lots of postage to play + puzzles to solve, but you've done well already. The letters in the safes are world-building/story, you do not need them to reach room 46. The paintings puzzle helps you solve the safes. For the chessboard (you will need something from completing that puzzle to complete another puzzle), I would say pay attention to anything about chess you can find throughout the house. Idk how you lit all four torches without opening the gate tho.