According to the app details on iTunes, it’s only 3.1MB, so 16GB is more than adequate. The speed of the iPad (iPad 1,2,3,4 or Air) and quality of the networking gear will have more of an impact on the performance of the app. Be aware that there’s supposedly an Apple Announcement re new models of iPads (rumoured to have more RAM) on Oct the 16th (and if previous experience is anything to go by the new iPads will be released a couple of weeks after that.) It might be worth waiting a couple of weeks to either get the new model, or see if the current models end up discounted.