Creating a LOOP function?

HI all, im building a arpeggiator and was wondering if there is anyway in which i could incorporate a loop function so that the arpeggiation would constantly be looped until a stop button/bang was used?

Also im would like to have a random function so that the the arpeggiations could be selected at random but with out the need of the user having to push a button to select a random output, i wanted to have it so that when a key is pressed on the keyboard it is automatically randomised, any help would be great thanks guys.