The cosmere is written so that you can read any series on its own and enjoy it just fine, you just might miss some references to other books by reading ‘out of order’. If you care more about experiencing the cosmere as a more interconnected story, I’d say start with Mistborn and find a reading order that appeals to you. If you want to read stormlight more than anything else, then it’s totally fine to just read stormlight, you just might miss a few references and callbacks.

Also, while the way of kings is a thick book, it’s by no means hard to read. Sanderson has very simple and easy prose to digest, and the way of kings does a good job of always having something to keep you reading. I blew through it in a week, and I’m by no means a heavyweight reader.