I am planning on getting a MacBook around late August and was noticed that there is a discount on Parallels until the 15th July. Can I buy Parallels now, but actually begin to use it in two months or so? Are there any problems in doing so?
You can buy and download it now (on any machine, Mac, PC or whatever) and start using it on your Mac any time you like, even in ten years (if Intel Macs haven't been replaced by the next big thing). There will not be any problems you wouldn't encounter if you started today.