Welcome to the forum.
On the Champion Iridium plugs, read this.....
Champion Irridium plugs - DON'T!!!
Whatever you use, yes, gap should be .040in
On the synthetic oil; 5W30 if you live down south, 10W30 if your temperature see colder weather. Are you still covered by a warranty? If not, stretch your oil change intervals to 4, 5 or 6,000 miles if you go to full synthetic.