Morning Darren
Welcome to the Forum
To be fair we don't see to many Mini questions which actually points to them being pretty reliable
Get a good BMW/Mini capable Diagnostic reader they are well worth it BMW INPA/ISTA is best obviously as it gives dealer level access plus Workshop Information and many other functions. There are several alternatives these days iCarsoft, Autoligic, Foxwell are a few others
www.realoem.com is an online Parts List if you enter the last seven digits of your Vin into the search box it will call up your model then search the sections for what you need. Having the correct part number means what ever you buy will fit (obviously) but also allows a good search for best prices. There is also a Register of BMW Specialists in case a Garage is needed and a Register of BMW Specialist recyclers
Normal buying rules apply Condition, History, History and History make sure everything works I mean everything if all good then I hope you enjoy your Mini
Dave