MD5 is not used anymore, not a strong type of hash algorithm. You should use SHA-256 instead. Overall algorithm would depend on your application, for example if you use a captcha I would recommend only using a hash algorithm to store the passwords. But if you don't you could use salt, it is the ultimate answer to brute force attack.

Objective - C could be challenge for starters but XCode is a very useful IDE and once you get the point Obj - C is fairly easy as well. I agree with copying successful apps to make money in short time. You can check Angry Chicks App as an example. Its a joke but very successful. If you want to develop 2D games for IOS and Android at the same time, I strongly recommend Corona SDK, coding is in LUA language, which is very easy to learn. SDK is perfect and physics engine rocks. http://www.anscamobile.com/corona/[^]