I agree with what some have been saying here. Learn to fly a bit before you add the distraction of a GPS. The Navy paid for me to get instruction before I went to flight school. Flew Cherokee 140's out of Santa Monica while I was in College. It is nearly IFR there from the smog most afternoons. We never got lost, just follow the roads. You need to learn to navigate by sight before you depend on the great technological wizard in the sky. For a backup you can run Foreflight on an iPhone as well as the iPad. So if your worried about getting lost, it is a fine backup. There are equivalents in the Android world as well.
I have the iPad, the iPhone and a Garmin 796. I also had a 496 in the Birddog. As mentioned the iPad is too big for yoke mounting. Well not too big, but obscures a lot if you mount it on the yoke. The 796 is a much better size for yoke mounting. I mounted the 496 off to the side in the dog, as it had no yoke, and mounting it on the stick was plain stupid. The 496's small size worked well in that cockpit. I did find the buttons annoying, especially after getting spoiled by the 796 touchscreen.
External GPS units are totally superfluous for the iPad and iPhone, unless you have an early iPhone mark 1 or an iPad 1(no internal GPS). I can lay the iPad or iPhone on the co-pilot's seat and run Foreflight in the Caravan cockpit and not have any issues on reception. It sounds dumb, but I run all three, one with weather showing, one with waypoint data and one in moving map. Why not. I got a Griffin mount for the iPhone that has a clear vinyl square with a mount in the center for a few bucks. It actually will stick to the plexiglass of the windscreen on the Caravan. So the iPhone goes there with field data and frequencies. The iPad runs in moving map on the seat and the 796 is doing it weather thing with XM.
If I was in your situation, I'd start with the iPhone and Foreflight. Unless you wanted the iPad for other things, I'd wait until I was good at flying before I bought up to something else. At least the iPhone is a phone that has a lot of utility and if you find that flying isn't going to be your passion for life, you didn't waste a bunch of cash on a specific aircraft item. The 496 and even a 196 are just fine to do navigation as well, better price than the other stuff, small to boot. I still think an iPhone trumps them both. Besides the iPhone 5 is just around the corner with an even (apparently) bigger, higher resolution, display. Pack a sleeping bag and some snacks and get in line now.
Griffin Mount, cheaper on eBay:
http://www.amazon.com/dp/B004PY09YY/?tag=hyprod-20&hvadid=15475785219&hvpos=1o2&hvexid=&hvnetw=g&hvrand=6765080441578422205&hvpone=&hvptwo=&hvqmt=&ref=asc_df_B004PY09YY