No, you're doing great! Leave the filter on, just don't let it run dry of course, lol. I hope you don't think this is going *speed up* your fishless cycle, its not. Its just hopefully going to help get you back to where the feedback makes more sense and the process is sort of "reset." ...Of course I should say, we hope the lowered NO2 and NO3 -will- speed things a little!
Glad you're working on the Python idea. Acually the whole reason I liked the original product itself was because of all the custom lengths and the brass adapters for all types of strange bathroom faucets etc. I've probably misguided you about the temp matching - I was just saying it to try and keep things as nice as possible for the bacteria but in a big tank and a situation like yours you should be worrying about that detail. Your heater will be getting good old cold hose water up to where it needs to be overnight and that'll be good enough. Tossing in some warm if you can will just help it along, no worries. You'll want to bring it back up to 84F/29C.
Agree with Geoff (he's got a good head for this stuff!) that its no problem having your good fertilizers in there, in fact it'll probably help to ensure that the bacteria can get a little iron when they want it as that's one of the things that its known they need, along with enough hardness in the water for them to get a little calcium! My personal pref is for the Seachem Prime water condition or perhaps Amquel+. I like these for beginners for the duration of the fishless cycle and however long it lasts after that but then after the colonies are robust I recommend switching to pond conditioner products as cheaper.
Hey, don't get down about it. One of the reasons you see "repeat" people here is that everyone ends up feeling they will do some things differently "next time." Its only after you've really experienced it that you'd truly know to allow a big bunch of time for the whole fishless cycling and setup thing. These bacteria are just plain slow sometimes! Don't worry, you're big tank is going to be great!
~~waterdrop~~