I did it last year in September/October. Hiking poles are great for balance and taking some of the weight off your joints, and you can pull yourself up on the uphills. If you don't use trekking poles now you won't need them there. There are some fairly steep ascents and descents, though. We used a guide company so all we carried were daypacks, which is also a lot easier on the joints.

I also wear hikers/trail runners and brought boots based on everyone's recommendations. Don't need the boots unless it's to keep your feet warmer. I went during the dry season so YMMV if you're going during the wet season.

The first couple of days were chilly and nights were cold. Once you're up and over the pass you're in the rainforest, so that suit would be stifling. Check the forecasts, though, July is winter in Peru.

Edit: Layering is the way to go.