I use either the ipad or the A4 as effect processors and for both the process is similar.
1- Connect the MPC Live output 3/4 to the mixer or effect, then in the Live either route the output of a pad/program to that output (Or you can use a send, but for resampling I prefer to record the full wet signal that I can later mix back in as a layer). Mixer or effect output goes into the MPC Live input
2- Easy-peasy, just plug your effect how you want then the final effect or the mixer are plugged into the Live input
3- Same as 1, I don’t think it makes any difference.