Getting random misfires.. Do minis have shared or single coils? Maybe wasted spark?

where could I start?

 

300 is for random misfire and doesn't identify a particular cylinder.

If you have an individual cylinder misfire then you can swap the plugs and coils around to see if it moves.

But not a bad start to do plugs
https://www.waymotorworks.com/spark-...-cooper-s.html

If you need coils only go with the OEM as they will put out the actual correct spark, aftermarket usually put out less and sometimes don't fit
https://www.waymotorworks.com/direct...9-r60-r61.html