Spotty new leaf & black coloration at base of mini Phalaenopsis

[FishyPlanter]

Hi everyone! I received this phal as a gift a few years back (first and only orchid), and have been following basic care instructions, but now am trying to learn more to give it a better life (reading articles from orchid societies and posts on forums like this one, etc.). I've noticed some changes for the worse over the past couple of months and am hoping I could get some advice on my specific situation.

It's been in its container from a big box store since I got it (sphagnum moss in plastic liner with drainage hole in a terra cotta pot). It hasn't flowered in over a year and the newest leaf looks unhealthy (black/brown spots). I started to repot it into a container with better aeration and orchid mix, but all except maybe one of the roots that were in the moss were dead (I removed them, the whitish root in the photos is the one remaining). For the short term, I just have the plant suspended over water to keep it humidified and am soaking the roots for about 15min/day. But I am wondering:

1. Do I need to remove the newest leaf? I am not sure if it's rot or not, but if it is I don't want it to spread to the crown (but on the other hand, don't want to take off a leaf if it's ok!)

2. There is some black on the base of the plant where it was sitting in the sphagnum. Does this require intervention? It is very firm, not mushy at all

3. Where do I go from here in terms of re-potting? Re-pot with the one (maybe) living non-aerial root in the substrate to anchor it? Something else?

I'd really appreciate any advice!