Break it into parts and go after the most important things only. Don’t complain about things that didn’t happen in the end (being offered a 2 day later flight). Keep things at the level of “i had two delayed flights thst Ultimately made me x hours late. On top of it, your delays caused my luggage to misconnect, which caused me a lot of aggravation.” I wouldn’t complain about the seat because it’s annoying, but probably the least annoying part of your day.

Any baggage delay financial claims go to KLM.

The internet complaint goes to the WiFi company.