Hi everyone !

I'm being desperate right now, as I've never been that much inside an engine.
For context, I bought my 2008 4.2 NA XK (197000kms, 1 owner), and done so far a couple thousand kilometers with it. Lately, I've had the classic broken thermostat housing, and I proceeded with the replacement of the housing, water pump plus a couple hoses on the way (including the small vacuum hoses which broke during disassembly).
By doing that, I also removed the intake manifold without removing fuel rail and injector, just disconnecting the feed tube and emptying the remaining fuel inside the line. Many gaskets were removed and replaced (intake steel gaskets, green rubber one, etc)...
I assembled everyting again, started for the first time roughly (expected since I emptied the fuel rail), and from this moment, it runs on only 7 cylinders. The culprit seems to be cylinder number 7.
I tested the #7 injector resistance (15.4 Ohms), so doesn't seem like it's faulty. I haven't tested coil or spark plug yet, and it'll be the next thing I'll do (swapping them with another cylinder).
Right now, car throws various codes: P0307, P0316, P0171 and P0174 + EML.
Short and long term fuel trims are maxed out (28%/20%) on both banks, and O2 sensors do not have same values on each side (one is 0.025V, other one is 0.035V).
When I disconnect the injector #7, car runs a little rougher, but when I disconnect another injector, car runs really rougher --> I understand that it's not related to the harness or connection since it's generally an on/off kind of defect.
Before disassembly, car ran absolutely fine (except temperature reaching 115-120°C for a few minutes only, amber warning (no red)), and I can not comprehend what could be the culprit. Just a perfect coincidence or did I break something on the way ? I did not touch anything ignition related.

What are your thoughts on this ?