ToDs were a thing in evo last year, but since then, the undizzy system has been implemented. This doesn't reduce damage of attacks, but makes combos WAY SHORTER by allowing the hit character to burst out of the combo when the undizzy meter is full. On average, it's about long enough for three ground strings and two air strings. What you have to watch out for now are resets.
As for the learning curve: It's as steep as you make it. For single player mode you can play through the story and arcade (don't take beating the final boss seriously, she's supposed to be stupid hard) on various difficulty settings, which will allow you to practice hit confirming and combos. If you hop online, you'll probably run into some very good players, who, as with any game, will completely destroy you. If you're not the type who enjoys learning the very hard way, you should be able to find some other beginners on this forum to play with. Personally, I recommend being able to easily beat arcade on nightmare (sans final boss) before trying to play online. For me it's frustrating to play other people before I'm really comfortable with a character's movement.
Good luck, and I hope you have fun with the game!