Hi lovinglooper !
Glad you Love the app

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I have not tried iRig + dynamic mic, but I had some feedback about it being very quiet. Which can be understood, the signal level of a dynamic mic is low and the iRig tends to pad down the input to cope with hotter guitar signals. So if you have a preamp, it would probably work well, but without you would have to deal with low input volume. IK has presented the iRig mic :
http://www.ikmultimedia.com/irigmic/features/that seems to be well design for the iPhone. It's an electret mic, and that's the kind of mic the jack input of the iPhone has been designed for.
You can always run the iPhone through a mixer. Its audio output is nothing fancy, so it will not be a problem.
For the more complicated things you want to achieve, it may be possible.
First you would need a stereo input for 1) and 2), that disqualify the jack input. Except if you put a mixer before it. Remember that Everyday Looper records and playback in mono only. One dock device would do what you want for 1) and 2). It's the Alesis ProTrack. But unfortunately, it seems to be discontinued, and it worked only on pre-4th generarion devices. The Sonoma GuitarJack might be a solution too, but it has the drawback of requiering apps to implement a "control panel" to work at its full potential. A control panel that Everyday Looper does not implement (yet ?).
For 3), you could just use a simple jack splitter, if you just want the same output on P.A. and in your monitoring headphones. If you want more complicated routing, like only track 4 on your headphones for exemple, it's not doable yet. Because Everyday Looper manages only a mono output. When/if I implement stereo management, you may have workarounds by splitting your stereo output to 2 mono.
One device that I'm quite excited about is the Alesis StudioDock. It's like the big brother of the ProTrack, but it's for iPad. It has a dual input too, even if I'm not sure you can "merge them" from the device to a mono signal like on the ProTrack.
So no perfect solution yet, but we are all making progress (hardware manufacturers and software designers), so it's getting in the good direction ^^.
Cheers !
Raphaël