Jazzy, the decision between a German, or French frog is one your teacher can advise you on... this has everything to do with grip type, and playing style. A 3/4 or 4/4 size is going to be a fractional difference of length of the bow stick. (and possibly width of the hair hank, though I can't imagine this being much)
As you'd expect, with higher quality bows, so goes the price. Best advice I can give is this: Try a lot of them. Bows are a very personal thing, and finding one that feels 'right' and balanced in your hand is quite critical. I have a nice one that was a gift to me years ago, and had been told it was a very good quality antique bow, of pernambuco, octagon stick, French frog, known maker, etc. One day I got to play with a modern carbon fiber bow, and WOW! It was a huge difference. So much easier! I almost wished I didn't know there was better out there.
Now, paging Casey Vancouver.