Sorry to hear of your troubles sjolliff,
You looked to be coming along ok with progress from your ammonia processors prior to the MM addition. Frustrating! I guess that's some of why this forum exists, because these startup processes are not all just a canned simple thing, they can be a bit of a black art sometimes.
rabbut has been an excellent advisor the whole time I've been here on TFF, so I'm sure the advice he gave you would have been spot on. It certainly does look to be a mystery why you were getting no signs of nitrite activity going on 30 days. I certainly wouldn't be worried about plants, the most effect they usually have is simply to lower ammonia and/or nitrate(NO3) a bit sometimes, leading to some confusion it that's not taken into account. Although plants can technically absorb a bit of nitrite(NO2), that's said to be quite rare and virtually never reported to be a practical consideration in terms of our fishless cycles and test kits.
I forget, have you ever picked up a GH/KH kit? They're quite helpful if you're thinking of using baking soda to increase your KH>pH situation.
~~waterdrop~~