What about iPad3 64GB for R3700? Not mini.
Do not even touch the iPad 3, Apple released the iPad 4 around 5months after the 3, the 3 had heating issues, and an old SoC that could not cope. If you are looking at old iPads then a 64GB iPad 4 is the lowest you should go, the iPad 4 at least had the A6X CPU with an incredibly powerful GPU, that's why it's still able to run the latest iOS with no issue, the iPad 4 was also the 1st to come with the Lightning Port and has the biggest battery found in any iPad, it is the heaviest of all iPads. I have iOS 9.2 Public Beta on my iPad 4 running beautifully.
At the end of the day I'd say get a iPad Mini 3 with more storage, otherwise do not settle for less than an Air, if you go older than Air do not go older than iPad 4.