If you hover over the picture on the Postbag from the Hedge page, the alternative text says "my name is in this Postbag," possibly hinting at the fact that the Chaos Elemental's name is somewhere on the page.
In the page's source code is a hidden line saying "Peter, I know you are looking in my suitcase. BTW - the gas is on at your house." This was a note from the Chaos Elemental to Postie Pete.
Note 2: Each of the requested "items" has a missing word in common: Red, Axe, Chaos, Dwarf, and Machine. The words "I forgive you" are written faintly on the opposite side of the note. This note hinted at the Forgiveness of a Chaos Dwarf quest, which had already been revealed through Development Diaries at the time of the Postbag.
Note 3: "Mentor a bandwagon" is an anagram for "Rag and Bone Man Two." The "No. 156 in the world" revealed that Fur 'n' Seek, the sequel to Rag and Bone Man, would be the 156th quest.
Note 4: "Hardens South" is an anagram for "Use Shorthand" and the text appears to be written in Teeline Shorthand. The translation is "Uv b wd abt Sl Ws. Nmd is tb frd." Transcribed it says, "You've been warned about Soul Wars. Nomad is to be feared." The note is signed "zzz" with a squiggle in parentheses that translates as "imp" in shorthand, indicating that the note was written by Zimberfizz, Nomad's imp. In the same Postbag, Zimberfizz answered a player's letter, expressing suspicion that Nomad has "some evil scheme in his noggin." This note hinted at Nomad's Requiem.
Note 5: Using the coloured arrows at the bottom of the "All in One Place" sheet as a guide: The letters to the right of the blue underlined letters are an anagram for Fishing, and the letters to the left of the red underlined letters are an anagram for Mining, indicating updates to fishing and mining. The names listed are famous rock and roll musicians. All the musicians on the right are living, and all the musicians on the left are dead. The final name, "Caverns," refers not to a musician but to The Cavern Club, where all of the named musicians have performed at some point--"All in one place." This note hinted at the Living Rock Caverns.
Note 6: Morse Code for "3" is found under the "Breakfast" heading. The symbols of the listed elements (Os for Osmium, P for Phosphorous, W for Tungsten, O for Oxygen, Rh for Rhodium, and K for Potassium) can be rearranged to spell "workshop." This hints at the upcoming Elemental Workshop III quest.
Note 7: When one looks at the layout of the Temple of Light, it marries up exactly, with the lines and dots in the Boxes section. This was a hint to Within The Light. The title, "Boxes," is written in blue, indicating that the quest was in the "blue boxes" stage of development (explained in New Dwarf Quest: Coding and Writing) at the time the Postbag was released.