Blocking out "The Sewer"

Starting work on "The Sewer" level and, for the first time, I'm starting by doing a blockout rather than just dive into building so I can make sure the mechanics and the timing work properly first.

An overall goal for each level is that the challenge should come from ‘puzzle’ not from ‘dexterity’, though remembering required actions / timing on second / third iterations of loop can be part of the challenge.  I want the game to be accessible, so far it just needs direction input to play with the 'end loop' button being optional.

I've also set myself the following criteria for any level:

1. Level should be completable with 0 bonus chests with 5 seconds remaining
2. Level should be completable with 3 bonus chests in 2-3 seconds remaining
3. No character should have ‘nothing to do’ for more than 3 seconds (unless loop ends early, still try to avoid)
4. Max iterations for 0 bonus chests 2 and 3 for all chests.
5. At least 2 characters should use unique skills per level even for 0 bonus and at least 3 characters should use unique skills for 3 bonus chests

Rules 1 and 2 are to ensure that the levels can be completed with 'time to spare' and that completing without the bonus chests should not feel rushed once you work out the puzzle / mechanics part of the level.  3 chests should be more of a stretch but still something players can come back and try and improve on.

Rule 3 is something that most of the existing levels already break.  15 seconds may not feel like a long time, but it can start to if your running a loop with a character that has something to do in the first 5 seconds and the last 5 seconds but nothing in the middle - you can't skip the loop so you end up just running the character round in circles.  Bonus chests help, but they should involve more than just running to a distant part of the level.

Rule 4 needs a little more explanation.  Some levels require you to loop through all four characters multiple times in order to complete the level if the hero can't complete all of their tasks until after another hero has unblocked them on their loop.  I may relax this, but needing to go through all the actions of all for characters for too many loops may start to feel like busy work.

Rule 5 The heroes are special because of their skills so each level needs to show them off.  The sewer will introduce some jumping and climbing for the rogue and may have the wizard start to use some combat magic too to keep things interesting.

The rules and the time constraint make for some interesting challenges when putting a new level together - so blocking out like this is becoming essential.