I would change the oil and filter and cut the filter open and go from there
As far as putting synthetic oil I would run regular oil for at least one oil change(1000+ miles)
I run my motors at least that far before going to full synthetics, don't forget to retorque the intake bolts several more times after driving it each time to warm it up until it takes a hard set, that will help the intake gaskets from seeping oil into the intake ports