That depends on how you're defining "bastard sword".
If you mean it in the sense of a historical longsword, a very average size would be a 36" blade and 12" hilt. They can be bigger, or smaller, but a total length of 46 to 48" is a very "normal" size.
If you mean more of a hand-and-a-half style bastard sword, then in my mind that would mean something that's a little closer to a single-handed sword, but with a longer grip, so a little on the smaller side for a longsword. I'd probably put the blade length between 30" to 35", and maybe a hilt size of 10".
BTW, I'm saying hilt sizes in terms of the total length of the hilt, including the pommel.
My personal preference for a longsword is right around that 36"/12" split, for a 48" overall length. I have to admit though, when they're a little smaller, they can be really agile. Any bigger, and I think they start getting into the "greatsword" category.
But since swords can be (and were) pretty much any size, it's entirely up to you as to what suits your needs.
BTW, congrats on your new toy! I'm sure it'll be a lot of fun!