Just go by the MM.
If you end up doing oil changes at anything less than 5k miles, there will be no substantive advantage to using synthetics. The Group II+ base oils used in modern 5W-20 conventionals are so close to synthetic performance, for anything but very extreme situations (very cold, tracking car, very long oil changes, turbo), there won't be any difference in engine wear and cleanliness. Particularly, with a small 4 cyl normally aspirated engine.