getting a new puppy

Question
We currently have a rescue dog who we got 4 months ago. She is 6months old now and we all love her so much. She is a collie crossed with a dalmation and is extremely intelligent. Due to her high energy levels and intelligence she takes a lot of stimulation and apppears calmer when she has interacted with more dogs while out on her walks. She is normally well behaved in the morning after her walk and sleeps but then after her afternoon walk she won't settle and constantly wants to play. It isn't always possible for us to entertain her and although she does play by herself for a while she always comes back to us looking for a playmate and continuously barks at us until play. She repsonds well to commands, can be left for relatively long periods of time, is good on her walks, loves other animals and having cuddles with us, and hasn't yet met a dog she doesn't like - although she gets a little scared when shoved over by huge dogs!
We are thinking of getting a playmate for her as she needs someone to play with so she isn't always bored. After long discussions we are still trying to work out the best age and breed of the dog to get. We have seen a rescue dog, not too far from us, who is a lurcher crossed with a dalmation, 6mths old, a girl, responds well to basic commands and is clever. We are sure this would be a great match as it is not really calming down that our dog needs but a playmate to keep her stimulated, and this other rescue dog will be able to keep up with her energy levels and is more or less an equal.
Obviously we would want the dogs to meet first but we're just wondering if this dog would be ideal for our existing one or should we re-think the age or breed. Any help and advice will be much appreciated.

Answer
I would not get two females who are close in age, and I would not rush into this yet.  Since you have only had her for four months, I cannot imagine that her training is complete yet.  And, before getting a second dog, you want full control over the first, otherwise you might just end up with double trouble, not the idyllic play you imagined.  The reason for not getting two females is that if they don't get along things can get really ugly, and a six month old dog is not mature, which is when you might see this rivalry develop.  Females can kill one another, while males are generally more ritualistic if they have a tiff.  I'd be more inclined to say that a subordinate male would be a better choice for a newbie to multiple dog households.  That said, I have three females and one male here;-)  At any rate, you need to understand that some dogs do not want a playmate, no matter how much stimulation they need.  And, keep in mind that some shelters and rescues will label a dog part "lurcher" (all tha term means is that the dog is part sighthound) to explain away rose ears, when the dog is really part Pit Bull.  Not that it's awful to have a Pit, as a breedm they are lovely people dogs - but they often do better in single dog homes, or with a dog of opposite gender.  You almost never want two female Pits (remember they are terriers, and female terriers, when they dislike one another, get really serious sometimes).  If it were me, I'd look for a male, or an adult female that is more subordinate than your current dog and widely spaced in age (example: my females' ages are 19, 8, and 3).  If you want some additional expertise on multiple dog households, get a copy of Patricia McConnell's "Feeling Outnumbered?" It's inexpensive and will give you a new perspective on living with more than one dog.