You're right! I would add one something: "Merci de" + [INF] can sometimes be used as "Thank you for [doing something that's is not finished]". So, if someone is currently helping you, you can say "Merci de m'aider", and if someone helped you, as you said it's "Merci de m'avoir aidé". Also, "Merci de" + [INF] in the meaning of "Thanks in advance for..." is often used by companies to be polite with their guest, we often hear "Merci de patienter" or "Merci d'éteindre vos portables"... But when it's used in the everyday life it can sometimes sound a bit sarcastic, for example, if you're struggling, and someone is not helping you, you can say "Merci de m'aider" could mean "Help me, what are you waiting for ?" So if you want to say something more friendly, maybe it's better to say "Peux-tu m'aider s'il-te-plaît ?" It all depends on how you say it, and what is your relation with the person you're talking to. I hope I've been clear.

Hello, oui c'est tout à fait ça, tu as bien compris.