We have the same truck other than the motor. Power is not a problem for my EcoBoost. You're 5.0 has almost as much power. We are towing a Cougar 29BHS. It's 7,000 empty. I wouldn't go much heavier than that. I'm closer to 8,500 loaded up. If our daughter wasn't still living at home, I'd go without the bunkhouse. The Cougar is a real nice trailer but their smallest one is 26' and still about 6,600 empty. If you're wanting a nicer trailer and can live without a dinette, check out the Grand Design 2250RK. I looked at Grand Design and they're really nice. They just didn't have the floorpan that was perfect for us at the time. The Cougars have king size beds. My wife and I are both tall so we like that. That 2250RK has the walk around bed and theater seating. It's also 5,500 pounds dry. Easy for your truck. It would be a perfect weekend getaway camper for a couple I think.
I don't know if you've towed anything with your F-150, but it's a great TV. I tow my trailer between 65 and 70 on the highway. No problem maintaining speed up long hills. I do have a ProPride hitch and airbags in the rear for a more solid feel. But it's no problem. I'm confident I could tow even more but the experience would probably be less enjoyable beyond what I'm doing now. You're 5.0 only has slightly less power than the EcoBoost so, you'd be good there too.
2019 Keystone Cougar 29BHS
2018 Ford F-150 Lariat w/3.5L EcoBoost, 10 speed, Max Tow
ProPride 3P-1400 hitch