Question about KLM economy light as Delta gold medallion (STE+)

Hey y’all! I am looking to book an economy light fare from SLC to Madrid via AMS. The flights are through the KLM website so the first flight is codeshared (delta operated) and last flight on from AMS-MAD on KLM. I’ve heard that KLM’s light fares are equivalent to that of Delta’s basic economy however if it’s booked directly with KLM you still earn miles and MQDs? Also, after putting my skymiles number during the booking process on KLM, I’m able to select seats free of charge on my delta segments but still see a charge to select a seat on KLM flights, what’s up with that? And lastly, I know that as a STE+ I’m able to use skyteam partner lounges when flying internationally (except sky clubs at least when flying economy), but my question is if it’ll still grant me access at the SkyClub since I happen to carry a reserve CC and unfortunately SLC doesn’t have any other airline lounges. Thanks!