IMO, FP+ is always needed for the headliners and considering you're not going at a "slow" time of year, I'd say absolutely.
Then again, I only do headliners with FP+ (and before that, FP) because I don't stand in long lines. I'd rather skip a ride than wait an hour, but that's just me.
We're going at the same time and would never consider not taking advantage of FP. Even when we've gone during supposed "2" level crowds, FP is a great way to maximize ride time.
I don't know that there is really an "average" crowd level per se, so I'd probably call it more moderately crowded. It's not low crowds but not Christmas week either.
Thankss. I just got back from a trip June 26 - July 2 and the longest line we waited on was 20 minutes. That was to ride the land in Epcot and to meet Aladdin and jasmine lol. We really took advantage of easywdw and fp+. Come to think if it, I will def utilize fp+ again. It will be a little more complicated this time though because we are only staying 3 nights are on the deluxe dining and have park hoppers. Hard to know exactly where we will be at what time and hard to squeeze things in between dining ressies.