Right heater first! Lack of heat is probably the heater matrix gone, do check that it has a thermostat present in case someone removed it though! Sitting 1/4 is fine, nissans do that if unsure it should run at 85-90 degrees.
The temp will rise when you are towing as the engine is under load and working harder, if its only halfway dont worry, if it frequently runs into the red then get it checked! Other than that chill! If you tow frequently or plan to take off road, fit a pacet or kenlow electric fan as an additional, and put it on a manual switch!
Locking wheel nuts.....If the studs are undamaged, then just get suitable locking nuts to fit! They cost 15 quid and the work replacing studs on every wheel makes it very cost effective.
If they are damaged, remove hub and knock out with block and large hammer, when replacing make sure splines are lined up to avoid damage. If you need more detail let me know!