Although the USB audio interface is a really convenient way to have several preamplifiers, it doesn’t accommodate outboard hardware such as effects units. A better option would be a USB mixer, like the Behringer Xenyx which can use aux sends and returns to integrate processing and blend sources.
OTG is available for both apple and android, however its main drawback is lack of power for attached pieces.
Iphone is more proprietary than android and more expensive in accessories.
Groove book is a pretty cool app for getting prints of mobile pics, works ok for imported stuff too just be sure to clear meta data resize to 4x6" and rename "image", oh snap that's a bit, huh? Still at $4 for 100 single sided prints in a photo album delivered to the door. Worth it. XnConvert is a big help here for batch conversions and adjustments.
What you get every month with your GrooveBook subscription: Groovebook is an app that prints up to 100 of your phone photos and creates a beautiful 4.5" x 6.5" photobook and mails it to you monthly. Photos are printed on glossy photo paper and are perforated for easy removal. Groovebook ...