Thank both of you for your answers!
Matthew! You're the youtuber that made me consider Axoloti in the first place. Your tutorials and artistic explorations are equally awesome. 
The playback is not really an issue as you both stated. Good to know that the only extra bit of hardware seems to be on the sensor side (simple mic). I have started a design sketch, will probably upload it here later.
The box I want will do the following:
Record 4 sounds (preferably lets the user pitch them before saving) one sample at a time OR record 1 longer sample and uses a threshold to pick out 4 starting points, whatever is easiest to implement.
Create a rhythm. It will do so with essentially with just 2 knobs. Knob 1 sets the tempo. Knob 2 is a beat generator (macro control that generates rhythms, complexity increases at higher values). 4 individual pots for each sample, if the space is limited: 1 big macro knob controlling all the instruments. If possible write the loop as a wave file to the SD-card.
Besides the 2 knobs, there needs to be a few simple buttons for recording, previewing and erasing. I haven't decided yet on how many. But I want to make it as simple as possible (4 buttons will probably be enough). Making it very linear is not a problem, in fact that's the goal.
Perhaps an ADSR-envelope, 1-envelope for all 4 samples. Maybe just 2 knobs (1 knob for the attack, 1 knob for the decay, with fix 0 sustain, 0 release). Or a push-switch-knob to step through the envelope.
Recording process: 1) Record 2) Preview 3) pitch (optional) 4) save 5) autoload in a sampler and control with an adsr 6) overwrite repeat step 1-6 with the next sample. When 4 samples have been recorded, then and only then generate rhythm. When loop is saved/cleared repeat recording new samples (and new rhythm).
I have plenty instruments but my current interest is to use generative tools to spark new ideas. And I want to make it very limited.. recording 4 samples, generate a rhythm, in some way capture that loop and move on. Recall ability is not the goal here I'lll use the rhythms in a computer later on.
A few other options would be a input attenuator (knob), speaker perhaps? OLED? Another macro-knob that randomly loads a pre-defined fx-chain with a dry/wet-knob.
I will remember getting a fast SD-card and look into that Beatslicer patch.
I'm really at the beginning stages and my first language isn't english as you probably can tell. Again thankful for any input!. 12-15 pots/knobs should be max and there's always the possibility to use an external midi controller when prototyping I guess. To be honest, this is my first project and I have just started to understand analog/digital circuits.. so my knowledge and intution is limited. I have more experience in coding and a lot of years making electronic music in the box.
