Your original post indicated a LTFT of -25% bank 1 (presumably). What is it now? What are the current diagnostic codes? Suggest you do a reset in other words. Just in case whatever problems there are have changed.
You’ve done quite a bit of useful testing yourself. Be aware however that problems like this often end up requiring a fuel rail pressure test, noid test (injector pulses), fuel contamination test (e.g. water), and a compression test before the nature of the problem is discovered. Your idea to next look at the ECM connector seems sound.
If we went back to diagnostics 101, if a car owner reports (cranks ok, but poor cold starts, misfires), first ideas would be too lean rather than too rich. If you are certain it isn’t too lean, then battery/alternator, compression, EGR , fuel pressure, or fuel contamination.
O2 sensors don’t do anything for the first few minutes after a cold start. So the starting problems tend to say the O2 sensors unlikely culprits.
Air has to move through the engine easily and exhaust gasses out the tailpipe for it to work correctly. No chance of engine air starvation, right? Check the area where the air comes in, from there to the air cleaner, make sure no rodent nests or other debris accumulation. Good, strong flow of exhaust gasses out the tailpipe, right? You have 2 cats, but just one tailpipe, right?
hmmmm … My own experiences over the years with difficult to diagnose cranks ok but poor starting, misfires … fuel system or fuel pressure for the most part, vacuum system (or intake manifold) leaks causing “too lean”, ignition system after that, but never any ignition system problems on vehicle with electronic injection.
Feeling overwhelmed? Nothing saying you can’t ask a shop to do the diagnosis, then you can do the repair yourself if you like. Sometimes this is useful if only to get another set of unbiased eyes on the problem. Could be something obvious you just aren’t seeing b/c you think such a possibility is so unlikely. One poster here had set of difficult to diagnose problems, replaced this & that, no help, asked for a shop diagnosis, shop said problematic timing belt. Poster replaced belt and installed a new water pump, engine ran like a champ. (hmmm … come to think of it, with one bank out of sorts, the other ok, the cam timing mark alignment on the bad bank seems worth checking.)