Basing on what nyet wrote, it's still acceptable.
No.
As you said, lambda needs improvement, but it's on the safe side.
No, it's just not tuned.
Limp mode... Shit, i wasn't getting check light on, so i completely forgot about it. That's the point - i'm getting 16683/P0299 - all hoses all good, pressure tested my intake and everything seems fine. Is this faulty component in my hardware, or can be fixed in software? N75 seems to be working properly - before preload adjustment with proper idmx i had almost perfect boost curve.
Start with boost control linearization from scratch as described on the site. Especially after you changed the preload.
Your boost control looks like shit and most likely the problems are even worse on part throttle.
Also, when pressure testing, make sure to leave the intake manifold connected. If you pressure tested JUST the intake without the manifold connected then you could have a leak. Although the log does not suggest any major leaks, it is more likely the boost control is bad.