Tax is, or soon will be, less than the ph2.
Servicing will be around the £150 mark for minor, £200-300 for a major (slightly more for belts change) - see a specialist, NOT Renault!
Common maintenance is pretty straightforward for modern cars. The 172 don't drink a lot of oil or coolant, keep those monitored and check tyre pressures and you can't really go wrong. Electrics aren't wonderful but they rarely fail on a grand scale.
Best advice is have a search on here mate, lots of varioud guides to the 172...