If it has had one owner their details will come up on the V5 so a bit of detective work and you could approach them to find out any additional details.
if the exhaust and filter are standard there is a very good chance the ECU will not have been touched as it would give very little gain
The paint metal device will give the depth of the paint and is useful if you are looking to detail the car to a high finish but paint is paint irrespective of factory or damage repair finish so you could still be hunting the proverbial needle.
It used to be the case that factory paint finishes were slightly dimpled due to the drying process and repair paint jobs came up really smooth and mirror like in finish so if you looked along the car you could see the different way the light was reflected.
Giving the car a good hand wash, dry and polish will get you up close and will be able to pick out any small dents chips or cracks anywhere, the panels are quite thin so gentle tapping around the car may throw up some different tones if you are tapping on filler not metal