Visiting Argentina in April and voluntary work (Buenos Aires)

Hello Everybody!
I'll be coming to Argentina for 3 months, mostly to do voluntary work and travel around a little for a short career break. I plan to come in April, May, June which I guess is not ideal in terms of weather.....Was wondering if anyone could give me some advice - I could spend the first month in the South (before it gets unbearably cold) and then move up for a month in Cordoba and a month in Buenos Aires.

I would welcome any tips you can give me, especially in relation to weather conditions / travelling in Patagonia and Tierra del Fuego in April (...if I should strike it off my list completely or if there are specific recommendable local travel agents) and possibly some tips on finding a voluntary work experience in relation to development cooperation projects.

Thanks to you all and best wishes from the heart of the mediterranean!

Sharon