I would discourage a Weim. They are magnificent dogs, beautiful, but everyone I know with them say they are very attention needy. It works great if that fits with your family but my friends with Weimer's say they must take the dog for quite a bit of exercise or they tend to get bored and destructive.
My local shelter does a foster to adopt program. You can essentially "test drive" the dog. That might be a great option when bringing him/her into a house with cats and kids. Dogs act very different in the shelter, they are usually scared and unsure. It isn't uncommon for them to have a different personality after a few days of feeling safe. I know my shelter cat was the same way.
We have bought our dogs. It is a personal choice, for us we rescued in the past but she had a lot of health problems and it was very difficult emotionally. We weighed a shelter dog when we got Jens but for us it was the right choice to go pure bred. That being said, if I could do it again I would try to get a year old or so puppy. You know the terrible twos? Well that is about how a puppy is for at least a year. They whine, they have to be trained, they sometimes "forget" their training when they want to, they destroy things, they need to be watched very closely. For a newbie owner it may be more than you bargained for.
Amanda
2011 Specialized Epic Comp 29er | Specialized Phenom | "Marie Laveau"
2007 Cannondale Synapse Carbon Road | Selle Italia Lady Gel Flow | "Miranda"
You don't have to be great to get started, but you do have to get started to be great. -Lee J. Colan