Although voltages are "lowish" in general, but not sure if they meet the criteria of "low voltage" (all limb leads <5mm and all precordial <10mm).

Agree, P wave is probably sinus (but sometime when it is on T, you need to be careful).

In general, retrograde P waves (assuming originating from a backwave below His, is usually skinny as the activation of both atria occur simultaneously starting in the septum area (in the EP lab this is easier to see). However, sinus or other atrial rhythm usually leads to a wider P waves (typically has two components) as the atria are activated sequentially.