The screen size of the iPod Touch will probably be a limiting factor, since the apps mentioned are VERY good, but really need the screen real estate that comes with an iPad.
You might want to look at apps that let you custom-design a layout and add only the MIDI controls you need.
You might want to take a look at MIDI Designer:
http://mididesigner.com/ Concerning your iOS version ~
Is there a reason you have to stay at 4x?
You might be limiting yourself a lot of ways by not upgrading, and may be the reason some of the apps you tried do not work...