Hi Orm,
the first bit might be problematic : 1xIn and 2xOut considering the hardware of a phone tablet you often have on combo I/O, you might want to have an external soundcard plugged via OTG; but I'm not sure if this plays nice with libpd (even if there is no reason it won't).
otherwise everything in your list is ok.
DroidParty supports arrays and everyhting but you won't have the possibility to manipulate it from a gui. DroidParty is still supported on latest android versions, but it's not maintened anymore.
As for alternatives, you can try mobmuplat :
http://danieliglesia.com/mobmuplat/, or you can try ppp which may require you to code a bit (it's a fork of DroidParty with a few more gui options, a wifi midi clock and the end goal is to publish apps to the market):
ppp.mgsx.net