LinkedIn etiquette

First time really using LinkedIn and a little confused about how things work. I met a couple of people from some informational interviews (through my school's event) and sent them a little message when I connected with them. I was told that I should also send a follow up message but I literally have nothing else to say (since these interviews were only 10 minutes long) that I didn't already say in the connection request. A couple of them also messaged me after connecting with something along the lines of "nice getting to know you" or "thanks for connecting", should I be saying thanks back? Reiterate what I pretty much said before?

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