Just did the W trek and stayed at the Refugio's and reserved their full board in advance thru www.verticepatagonia.com and www.fantasticosur.com/en/ websites. We didn't feel we needed a guide, the trails are well marked and you can book the specific type lodging, made bed, bed or tent thru these sites. The trails are challenging at times, the wind gusts were something we had never experienced before.
The park has some spectacular scenary that we will never forget.
Definately book regular bus transportation to/from park from Puerto Natales in advance and remember to bring cash for the park entry fee and for the Pehoe Catamaran.
We met some great people that we saw from day to day.