I prefer TASCAM 424 mk I and mk II for better tape speed options, but mine are broken. I use loops but I also switch over to live channels. for feedback loops i usually just put the effect sends to the line in channels, but i've seen the headphone jack used too, I just burn things out too fast to want to try that.
For multitrack tape loops, the only advice I'd have is to make each channel distinct, each a different frequency range, a different texture, but make it complementary to each other, like adding colors to a palette to make a painting. It is better not to have every channel full sounding because they are just going to cancel eachother out, though I like having one channel that does this to cut everything else out suddenly.
Sometimes i record loops on the fly during the performance, but it's never usually good. Even when I saw a performance where one was using live instruments and one trying to do tape loops of the other, it just came out with not very engaging loops. It's not a immediate effect like the loop station, it needs more engagement and prep.
That I also "cheat" and use a digital delay on the fx loop to loop the loops to more loops, and use a pre amp so the signal will go over everything else since effects loops try to be tame to prevent feedback. Keeps the process more organic and interesting, and sometimes I'm practically making a song using the pitch control with it, albeit a very crude one which keeps me in the harsh noise realm hopefully (though I did steal that technique from someone who is released on Not Not Fun multiple times).
