Any good trail shoe will be okay for summer (hill) walking. You just need to make sure, just as you would do with boots, that they fit your feet.
The brand is not important, it's the fit and comfort that matter.
Do what Mike says. Keep your heavy stuff for the Ben. Shorts and trainers for the WHW. Get any lightweight hard shell that fits and ignore the marketing hype, buy the cheapest one that fits. Same with your fleece. A bum bag is a good option for your sweaty back issue.
Do a search on OMM Mountain Mover Product Manual and you will find one in Doctstore. If I was clever I could do the link thing, but I ain't. It won"t tell you much.
You have probably bought the one that I went for a few months ago on EBay, only it was listed as a Villain, so it went back.
I had an MM a few years back. Didn't like the hip belt or floating lid, much preferred the Villain, but each to their own.
Yep, what Shewie/Waldo said. A summer overnighter needs very little gear. You learn very quickly what your comfort level is and for me it was a Karrimat, for ground insulation to give a good nights kip.
Shelter? A weather forecast will tell you if you need one or not.
You can either mimic others or do your own thing.