Will it be easy enough to meet people [to hike with] in Puerto Natales?
I think it won’t be too hard to find hiking companions in Puerto Natales, it’s a pretty small town and gringos (including Europeans) are easy to spot near the Plaza de Armas (town square) or at your lodging, and they all are heading to the park. I’d be careful to find folks you’ll be comfortable with personally and who will have similar hiking speeds, etc. Maybe another good idea is to plan the association to be a bit loose (your own gear and food etc.) so if you aren’t compatible you could split up.