Thanks to John for this comment on the Korg PX3 Pandora:
“I have the Korg PX3 “Pandora” effects box which has many of the features you mentioned. It’s easy to use but has tons of features for later. I love it!
It’ll sample 8-16 seconds of audio and loop it, so you can learn riffs. It think it’ll even play it slower, to make learning easier. It has a number (40?) of pre-built drum patterns. Some even have bass lines which you can change the key!