It's not recommended to use full synthetic on a brand new motor, it's too slippery to allow the parts to "wear in" properly. You can buy special "break in oil" for rebuilds and such that's actually a little worse than regular oil to help things seat in faster, then change to whatever you want. Most bikes come from the factory with OEM brand 10-40 and yeah, the first oil change is usually pretty nasty, totally normal.
Even with the JASO MA certification, some full synthetics seem to be bad news for wet clutches. Mobil 1 4T seems to be a recurring culprit for clutch slippage despite being marketed as a motorcycle specific oil. I've used the Rotella T6 in all my bikes for years with good results. Diesel oil is more tolerant of heat than regular oils(good for air cooled engines), and contains more ZDDP(a extreme pressure lubricant), which is good for compact cassette transmissions.
The valves on a Grom are stupid easy compared to a I4 and should take maybe 20 minutes to do with basic hand tools and a feeler gauge. Even still, Honda bikes are known for rarely if ever needing valve adjustments. I'd check it after the 2500 mile "break in" period, and not give it much thought after that.