05-07-2012, 01:39 PM
Welcome to Mac-Forums
For starters, you will need an Intel-based Mac for app development. To use the newest SDK's, you'll also need to run the newer versions of OS X, which means a newer Mac.
Whether it's a iMac, Mac Pro, Macbook Pro matters only to you as far as your mobility and budget goes. You will want to get as fast a CPU you can afford, memory can be upgraded by yourself and you will want to max out the system..
Initially, you'll be using the simulator a lot and then going to the device itself, and not having enough memory will make things slow and cumbersome..
On my old Mac Mini 1.83 Ghz, I had 3 GB of memory and it worked well enough, when I upgraded to my current 27" iMac with 4GB of memory it was great..and then upgrading memory to 12GB allowed me to run all sorts of things with no problem..
How hard it is to make applications depend entirely on how much programming you know and the concepts that go along with it. If you don't know Objective-C, then you'll have to learn that first..
There are numerous posts about this in this sub-forum, so do a search and you'll get lots of tips, links to tutorials and books to read..