I learnt from the age of 11 on a full size one. I see little reason for anyone of this age or older to get a smaller one. Also you really need a teacher from pretty much the start, you will pick up bad habits that will be very difficult to get out of. Graded exams are good for something to work towards but you may not bother with them all, for example I did 1, 2, 4, 7 and 8.
Do you know anyone local who can play the violin? You really need to play the instrument before buying it to see if it is any good. As you haven't played one before this will be challenging.
Dominant strings will be good while you are learning as they tend to stay in tune very well. As you progress you may want to go in search of a string that suits you better but that's very far down the road. Strings don't last forever so they will need replacing every now and then (depending on how much you play, not just when they snap.) Get a good Rosin too, I personally use Laubach Gold. And remember to clean it off every time you play.
Get a scale book too. Learn G, D and A 1 octave to start with (memorising them but they are the same finger pattern just starting on different strings) so you can concentrate on intonation, bowing and tone production without worrying about reading.