Just play my friend, they are amazing. Yes you are kinda right, they recently combined them together into a thing called Hitman: World of Assassination, you buy that and you get it all.
My advice is to play all the tutorial levels and try to do most of the content and then when you hit the first proper level - Paris - do one or two "stories" with the full guidance on and then after that go into settings and turn the guidance to minimum and set challenges to the setting where it doesnt tell you how to do it, just gives you a picture and name of the challenge.
Not sure this would be your thing (maybe you prefer to go it alone in games) but send me a PM if you have a question about a mechanic or a potential idea/method thats not working for you and I'll give you clues as to how to get it done or an alternative that will work that won't spoil much. I've played the first two games for over 1200 hours in total so I know a few things.
I'll give you clues that make things make more sense or give you ideas but I wont tell you all the secrets/shortcuts unless you ask for them. For example you can use tools on things to make them dangerous or press buttons to activate machines but thats not the only way to do things and once you know the other way then it opens up a ton of possibilities.
Holy shit I'm so excited for you mate, I wish I could go back and experience it all again. Are you playing on PC or console? I'd be up for spectating you while you play, I have a PS5 so can watch direct there or Twitch for Xbox and PC (I'm guessing would be the easiest way).