Yeah Morphling (the water dude) is crazy good. At the last massive Dota2 tournament (The International 2, it was called) He was picked in every game by the Chinese, and then at the end of the tournament the other teams started banning him, coz the Chinese are too good with him haha
He's pretty hard though and not a beginner hero; you may have a hard time deciding when to use his skill waverform, as it's an escape mechanism, but it does damage, so you have to pick your battles so to speak. Also to use his ulti properly basically is like controlling two heroes at once, and he is also $$$ dependant so you'd want to learn about denying and lane control pretty good.
Game isn't too hard though. I recommend Venomancer, he's pretty easy and very good and fun. I recommend buying Mekansm if no-one else on your team does.
I don't know about LoL, but In Dota2 item choices are diverse, and important. You will learn that the recommended items are terrible in certain games, because the items you buy depend on whose on your team, what heroes are on the other team, what are you trying to do to contribute? For the first month or whatever, I'm sure just blindly copying the recommended items will be good enough though, and you will learn.
I'm taking a break from it at the moment but I will play heaps with you after November if you want.
Btw you'll need a Beta Key to play, which is hard to come by, if you need help finding one let me know.
I don't know how to make this post shorter sorry lol