WRT getting a dog there's no reason why you couldn't agree to do so and delay taking him until you move - taking him from where he is now and then moving again could be very distressing and disrupting for him and cause you both problems which may not be easy to resolve in the chaos and hard work of moving. You'll have enough on your plate without trying to settle a nre dog and ensure the removals men don't let him escape.
BUT more importantly, I'm worried. You say you've seen the dog advertised t buy... from where? If it's a breeder and they are responsible and reputable they won't LET you have him until you are settled, for good reason. I'd strongly recommend that you avoid at all costs one who would. Also, you must be sure that they will take the dog back if it doesn't work out... or then where will he go?
Worse still, if it's a Free Ads/Gumtree advert from a private home, please, DON'T. For YOUR sake as well as the dogs. What if it doesn't work and you have nowhere for him to go? What if the owner tells you that the dog is perfect but in reality he howls when you leave the house and pisses off your new neighbours, who complain to your new landlord? What if he bites you or any DC you have?
I'm a rescuer and I frequently see coming into rescue or worse, the pound or vet to be put to sleep, such dogs. A reputable rescue or breeder will offer lifetime's support and take the dog back at any time in his life if necessary. (Not that as a rescuer I advocate going to a breeder but if you must choose WISELY!).
And people LIE! They lie to us, experienced rescuers and they sure as hell lie to Joe Public when they want to get rid of a dog. A decent rescue or breeder will not rehome lightly, a reputable rescue will match the right dog to you and your family and steer you away from the unsuitable ones. All too often the private advertiser won't. He only has one or two dogs, he wants rid so instead of advising you on the right dog to have or saying sorry, that he has no suitable dog for you, he will tell you what you want to hear and once he has your money won't be there for you or the dog.
Another thing to consider... which would you prefer? A dog of DPs favourite breed which is unsuited to you and makes you and him unhappy or a different breed or cross which is perfect? Are you prepared to wait, on a rescue's or breeder's list for the RIGHT dog or are you so excited about having this particular breed that you will take a chance on the first one to become available?
I may be wrong and the dog may be from a perfectly responsible source and ideal for you... but please, please beware and think on what I've said. When I lost my Collie X girl I went to rescue seeking a similar bitch of about 4-6 years old... and ended up adopting a huge 9 year old long haired German Shepherd... the best dog in the world and perfect for us yet SO not what I'd been looking for!
If you can identify that my fears for you might be with good reason and you'd care to mention the breed I'll do my best to suggest or find a reputable breed club or rescue which might have a dog which WOULD be assessed and come wiith secure back-up and lifetime support. Lastly, never ever take on a dog without a homecheck... it's for YOUR benefit as well as his. It will identify and iron out problems before you start (maybe a simple thing like a fence with a hole or maybe to ensure that he is good with your cat) and cannot be underestimated.