you are pretty far ahead of yourself, though your enthusiasum is charming.
If you think you will spend much time doing dressage, then you will probably have more success all around in a dressage saddle, as opposed to a jump saddle. one can do basic stuff in any saddle, and a western saddle might actually put you in the closest alignment to what you would have in a dressage saddle. but, a dressage saddle itself will give a nice connection, and help you feel more immersed in the study.
There are tons of books , literally tons of books about dressage. IT is a very old discipline. check out any one that is handy. AT first, not much of it will make sense, but in time, reread it and it will start to come clear.
The other things, can all wait.