Free Economy Comfort on KLM as Delta Gold Medallion (+Other Questions)

First, yes i read the FAQ at the top, but that refers to PM and DM, and nervous about this EC free and paid combo that i've done. I am a Gold Medallion, and i was able to select several legs with Economy Comfort.

I am flying WAW-HNL
outbound:
WAW-AMS (EC free to select)
AMS-LAX (EC free to select)
LAX-HNL (EC free to select)
return:
HNL-SEA (EC free to select)
SEA-AMS (EC $59.50/ea to select, paid)
AMS-WAW (EC free to select)

All are in fare code (R), except for AMS-WAW, WAW-AMS, which is (L). The entire booking as sent to me by Delta is on KLM flights (though of course operated by Delta for some)

I followed up with a phone call to Delta, and they said my seats are confirmed, and they sent an e-mail itinerary (without seats, just flights... weird?). I followed up further at KLM.com, logged in, and all my seats and flights show up the same, and as confirmed. And e-mail confirmation also shows only flights, not seats.

Am i gonna get surprised at the airport, and find out my seats are not available, and i have the leftovers to choose from? Both sites confirm, and telephone confirmation as well. What, if anything do i have to worry about? It looks like GM get free EC domestic, is that right? I paid for SEA-AMS, is the price right? All in all, for $119 for two people, EC everywhere, looks great ^

PDF itinerary from Delta that i have shows seating assignments. I have this saved.

Thanks!