You can't really mimic a tape loop, without a tape loop the next best thing is using headphones on the tape deck to monitor, but that's not exactly the same.
As for an ADC, what's your budget? If I want to go from analog to digital I use a portable Tascam DR-100 which has a nice ADC and I don't need a computer just to record. I've also read good things about Korg's USB DAC/ADC.
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