Welcome.
This website has a pretty complete list of churches.
Talk to one of the priests at one of the churches in your area. A priest can best guide you on your spiritual path. Some parishes have classes, and some priests will work with catechumens one on one.
I can't stress this enough: Step one - talk to the priest. This is another one of those subtle differences between Orthodoxy and the rest of Christendom. We think of the priest less as a mediator, and more like a physician for our spiritual health. And just like a physician, everyone is treated individually according to their own condition.
As for some of your other questions: The best church for a beginner is the one in which you feel most welcome. Just like anywhere else, some churches are more welcoming of newcomers than others. That is why talking to the priest first is so important. If you find a priest who is interested in your spiritual well-being, and heartily invites you to Divine Liturgy, chances are his parish will likewise welcome you. I feel fortunate that in my area, all the EO churches are welcoming to visitors and newcomers (I happened to choose the Greek parish).
To my knowledge, there is no official EO catechism. There are a number of books which might act as such: Kallistos Ware's
The Orthodox Way, and Clark Carlton's
The Faith come to mind, but really, the priest can best direct your studies.
God bless you on your spiritual journey.
