My PUPPY Lucy is 5 1/2 months right now and this is my favorite stage that she has been in. She is still SUCH a puppy.... so playfull and cute, but now she is more fun, a little les work and worry, and way more cuddly. The longer they are with their mama the better. When they are taken to early it can cause problems later in life.....
5 months is a great time to get a pup. Plus, she will already have some training behind her which means you are not starting from scratch and I am sure you have heard that these little guys are a PAIN to potty train.
Goodluck with whatever you decided.
Oh- and someone else said this too: they are soooo cute at this age because they look really scrappy and scruffy because their adult hair is starting to grow in. PRESH!