I haven't actually hiked the Shores Lake loop. I think it goes all the way up to White Rock Mountain, right? I have hiked up there on the Ozark Highlands Trail, and it's a pretty tough climb. For a first trip, it might not be the best choice if you are not sure of your fitness level, especially if you haven't hiked long stretches uphill with a full pack before.

As for backpacking in Arkansas in the summer, it's not the best time to go, but I've done it. It depends on how clear the trail is, the temperature, and how well your bug repellent works. If you've hiked and camped in the summer already, then the main difference should be that carrying a heavier pack makes you hotter and more tired.

The Butterfield Trail is probably better for late spring/summer. I would think it is used a lot more, plus it's a horse trail most of the way, so it should be wider and clearer. And less strenuous.

I can't argue with Bill's suggestion to float the Buffalo instead, but if you are intent on backpacking and it's not too hot, it should work out ok.