Sounds/Music Sequencer App for iOS

I'd like to create an app that can play back loops synced in time with each other. Where some can be played/triggered 'live' and others can be clicked on/off until the end of the bar. So basically you can recreate/remix music quickly with good results with virtually no skill. Loops/sounds would be Apple Loops so have key/bpm info etc. this will also allow for easy changing of key and bpm. I have no design but would like a simple, retro tech type design. Other features I'd like to include aside from the main sound/loop playback include: The ability to record 'vocals' etc. yourself to add to the included sounds Twitter Feed Maybe the ability to see the loop and switch off slices/beats and manipulate them in different ways. Possibly add built-in audio effects to the loops or your 'vocals' like delay and reverb Save your mixes - maybe share via Facebook/Twitter... Drum Machine - it'd be great to have a step-time TR-Style drum machine to create your own loops from a selection of included sounds for kick, snare, hi-hat, etc. Export your mix as a iPhone ringtone The ability to update and add additional content/songs in future... If might be worthwhile to offer a cache system where users only download sounds they actually plan to use and have the others on a server as the sample data can be quite large. This might help keep the app lite and mean you could offer an unlimited number of additional 'songs' in the future too. There are lots of similar apps out there. This one would be interesting because of the content. The actual app can be based on many of the existing similar apps, that concept is fairly well established. We don't need to reinvent that wheel, you may have already done all the background work and just need to 're-skin' this. It's really more of a fun app rather than a full music production tool. So some of these ideas are very optional and certainly don't need heavy implementation. I've not gone any idea what a project like this should cost so I'm just leaving a wide window on the budget. I look forward to your responses!