10w40 as book recommends. More important to change it regularly than the actual brand. I use semi-synthetic and change it every 2000miles or so, many use mineral and others full synthetic. You'll get lots of opinions.
Haven't had to change it yet, won't until its at least 2 years old, but will go with Kawasaki recommendation. Some car specification coolants have additives that will trash a small bike pump, so take care.
Small amount of vibration around 4k rpm, but nothing that bothers me. Going with a 16 tooth socket will cut vibes at freeway/motorway speeds around 70mph.
No popping, take bike back to dealer and get it fixed, throttle bodies might be slightly out of sync. Check air cleaner, if bike is new, this is not the issue.