I'm still not totally clear on the encoding, but I am starting to thing the last 3 verses are broken into the first couplet referring to a letter and the last couplet referring to a specific "green" (arrow, goblin, hornet). The last clue (there's no...in..) reminds me of "there's no I in team'. I think the first two lines of the goblin verse (You won't find it in yourselves, but to express individuality it delves) similarly refer to the letter I (not found in the word 'yourselves', the letter used as a pronoun refers directly to individuality). I is the 9th letter and 59049 is 9^5. Similarly, I think the wordplay in the final verse's couplet could refer to W (twice intoned) and W is the 23rd letter and 6436343 is 23^5. I can't explain how "goblin" and "hornet" translate to 5, but I think I'd like to try those 2 keys on the 2nd and 3rd locks to see if they fit. If so, we could focus on the final couplet and see if we can make it fit for either of 'L', 'R', 'N' or 'E'