1. Is there any advantage to use K&N filter instead of the manufacturer's?
Pros and Cons.

2. Is a throttle clean up neccessary?

3. Is it going fully synthetic oil necessary?

Any other issues?

1/ The K&N flows more air and will last a lifetime. The drawback is that it needs carefull maintenance. I like it. Worth it to me.

2/ Not likely, but an inspection of the throttle plate would soon tell you. That would be as easy as taking off the clamp holding the inlet tube to the Throttle Body and looking in.

3/ Not necessary but very popular to help protect the engine better than dino, and possibly extend the oil change interval. It will also yield a horsepwer or 2 as a bonus. I like this mod too and use sythetic in all my rides.
The downside, as in the K&N filter is initial cost.

C.