In my opinion, skip the sippy cup!!!
I started my daughter directly on a straw and its been a life saver! Yes you'll have to supervise her drinking and I still do but all in all its been so much better! I don't have to take a cup with me anywhere anymore! We use them from time to time don't get me wrong, but she's learned so much better with a straw. And if it matters it helps wake their mouth up. If they have speach issues or you'd like to get a jump start on that, you can put shakes, yogart or even make them work really hard and put peanutbutter in it so they have to really use their little mouths. It serves so many purposes and makes life much easier!
Litterally when we leave the house, I take a diaper wipes and a snot rag and that's it! I have the smallest diaper bag out there and everyone wonders how. I don't have to carry a cup. I just pick her up something on the road if I need to or stick a bottle water in there for the both of us.
Its grose at first what they put back into the drink but they get better at that too... You may consider it! She's also learned that it is completely open and not like a sippy cup so she can't put it just anywhere and she can't tip it over. I still have to hold it for her 90% of the time but I'm tellin' ya its been a life saver so many times! Don't have to keep up with tops or lids or keep washing them because you'll never have enough... Try it and see what happens. I think its even better for their teeth/mouth too but I'm not positive on that so don't quote me... :o)
Its never too early either, just let them try it out and once you can get off the bottle even better! Its more like the bottle and having to suck to get it out anyways. the sippy cup is only like the bottle in that it has to be upside down. The sippy cup when you bite it it just falls out anyways... This way they learn not to tip their cup which is an ageless struggle with kiddos...
Just some thoughts, best of luck!!! ~T.~