Given the low mileage, I would make sure the DPF and EGR have been checked and the oil has just been replaced. If you aren't intending on doing either, I would have severe doubts about purchasing this car:
At least 10,000 miles of largely lengthy excursions (over 20 miles) and very few short trips from cold, or; Preferably much over 20,000 miles per year of mostly longer trips, to avoid DPF active regens, particularly if you can't keep driving until the active regen completes.
Examine the vehicle's history for evidence of DPF or oil dilution/high level concerns. Check out Honest John's reviews area for further information about difficulties, particularly the 'Good & Bad' subsection:
https://www.honestjohn.co.uk/carbycar/mazda/3-2014/
https://www.honestjohn.co.uk/carbycar/mazda/3-2014/good/
If operated properly and carefully maintained, it should run admirably and is a capable engine and vehicle. If your annual mileage isn't that high and you make a reasonable number of short journeys from cold, I'd hedge my bets (assuming you've already committed to buying the car and can't back out/swap to a petrol) and get the oil changed every 6 months to ensure those engine problems are reduced at the very least.
Also, 18in tyres are a unique (uncommon) size, and they are NOT cheap - Mazda dealers sometimes charge an outrageously high £150 per; you should be able to buy the same from the better tyre chains for between £115 - £130 installed. Low profile tyres have the normal drawbacks of being more prone to damage, lasting less time, and providing a firmer/noisier ride than higher profile tyres.